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  #21 (permalink)  
Old 08-19-2012, 3:13 PM
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Originally Posted by CCHLLM View Post
I concur with Jim202. Sudden alternator whine is a sign of something changing in the alternator and connected wiring.

If the symptoms were not appearing intermittently before the continuous onset, and a check of the physical wiring doesn't reveal a problem, the most likely candidates are the alternator diode array or the regulator, or both.

If the whine is a single varying whine like someone whistling, it's likely a single faulty diode. If the whine sounds like more than one person whistling in harmony, it's likely there's more than one faulty diode in the array. Either way, you need to replace the alternator. The faulty diode is leaking battery voltage to ground and the battery is being slowly discharged, which in turn will show up at starting time after sitting for a while.

To save yourself some time, go by one of the auto parts chains and have them give you the free alternator check. If the problem is the usual diode array leakage, you have found the problem. You can depend on the premium grade of replacement at most of these places.

By the way, one of the 2011 Tahoes in our family has had the alternator replaced this summer due to a bad diode array, and the 2008 Denali has had two replaced in 160K miles. All our vehicles have UHF mobile radios, and those have become our finest early diagnostic warning tools.
My thoughts exactly. In a former life I was co-owner of a starter/alternator rebuilding business. My alternator guy would take his pocket AM radio out to the vehicle- the cheapest, nastiest least selective radio he could find. If he heard whine, he would replace the diode array.

Alternators produce fairly high frequency AC and have between 6 and 12 internal diodes mounted in the casing to turn the AC from the fixed armature multi-pole windings into pulsed DC. The battery acts as the capacitor to level out the humps in the pulsed DC. If one of the diodes is open, the resulting null translates into noise in the DC system. The voltage output of the alternator may check OK, but the output amperage will be reduced. If the diode is shorted the negative pulse of the shorted diode will be counter to the flow and drop DC output. A voltmeter won't show the ripple (it's very, very fast) but an o'scope will. Depending on the radio, the noise could be getting into the power supply, speaker audio pre-amp or microphone sections, and not directly into the RF parts of the radio itself. This is evident when the whine is transmitted along with your voice- during transmit the energy is outbound and the receiver is effectively shut off.

At 1,000+ Hz the ripple is acting like an RF signal or lightning pulse, with all the weirdness that goes along with it. DC-wiring-thinking doesn't always apply, but short, clean and bright connections and multiple grounds are never a bad thing.

The ripple is an indication of a pending failure- pending being sometime in the next 0 to 60 months. You would be amazed by the number of non-radio equipped vehicles on the road with bad alternator diodes, charging the battery at 50 instead of 60 amps. Remember that once started, the car's electrical system runs off of the alternator- the battery is just there to start the engine and level out the humps.
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Last edited by jeatock; 08-19-2012 at 3:22 PM..
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Old 08-19-2012, 3:20 PM
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New alternator is on order, at least its a 15 min job and not to much money. Thank you to everyone that responded to this thread!
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Old 08-22-2012, 8:16 PM
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UPDATE: Changed out alternator and no change, still have the whine. I started following the factory ground wires around and came up with this:

There are two ground wires leaving the battery post, one 4-6 gauge wire running to the engine/starter area and one 10 gauge running to the frame. I removed the smaller ground to the frame and no change. I then removed a ground STRAP which runs from the engine to the firewall and 90% of the whine is gone. So im getting some where, just not 100% on what else is making the noise.

Im going to run a temp ground setup off the battery with new wire i have already and see if all the noise goes away.
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Old 08-22-2012, 10:17 PM
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I'm really interested to hear what you find if the firewall ground strap removal HELPED! On the alternator, did you do a diode bridge test on the original alternator before you changed it out? If it checked out OK, that would have indicated that the problem most likely lies someplace else. If the strap from engine to firewall made a big difference, I can only imagine there's a ground problem/loop somewhere. So many times there is more than one problem contributing to a situation. Remember, if this problem came on suddenly, something changed in the grounding and/or the hot side or in an electrical component.

Some suggestions:
I know this sounds crazy, but see if there is a small reference ground wire from a terminal or a plug-in connector on the alternator that needs to be attached to ground on the engine. That sounds nuts, but that was the problem on a particular brush truck we worked on a few years back. It went to the internal regulator and came out of the alternator harness about a foot back from the connector that plugs into the alternator which made it less than obvious.

Check and see if the body is grounded to the frame in multiple places from front to rear. If not, the firewall strap will have to be replaced because that is how the body gets its main path to ground and some other solution will have to be found. My Ford pickup has the body strapped to the frame across each body mount, and the bed is strapped to the back of the cab on each side and across each bed bolt, but this is a pickup with essentially two bodies mounted on one frame, so apples to oranges effects are to be considered here.

Once upon a time on a Tahoe that was driving a MaraTrac and its operator to distraction, we found that there was a firewall strap but no other body-to-frame grounding. Adding a body-to-frame strap midway toward the rear on each side at the body mount under the A-pillar, and at each rear corner mount stopped the problem. As to which one, if any of them by itself, would have done the trick, I can't say.

Check to see that the hood is strap grounded to the body on both sides in the hinge area. That can make a huge difference in a lot of cases.

I can't remember whether or not the GM stuff has a small ground wire from the battery NEG terminal to the inner quarter panel on the battery side, but many vehicles do have that, and may have a short jumper from the radiator support to the inner quarter panel on the opposite side as well. If not, so be it, but if it's there and not connected at one end, that doesn't help eliminate ground loops due to electrical piecesparts mounted on those components trying to find ground.

Any non-terminated or broken wire can create an antenna for radiating noise, so get under the truck and look for anything that looks wrong or questionable. If there is a question in your mind, find out what its status is supposed to be before you take any action or it may be the wrong thing to do.

Last edited by CCHLLM; 08-22-2012 at 11:23 PM.. Reason: because I keep thinking of things to mention
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Old 09-01-2012, 9:40 AM
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Originally Posted by jluisi86 View Post
UPDATE: Changed out alternator and no change, still have the whine. I started following the factory ground wires around and came up with this:

There are two ground wires leaving the battery post, one 4-6 gauge wire running to the engine/starter area and one 10 gauge running to the frame. I removed the smaller ground to the frame and no change. I then removed a ground STRAP which runs from the engine to the firewall and 90% of the whine is gone. So im getting some where, just not 100% on what else is making the noise.

Im going to run a temp ground setup off the battery with new wire i have already and see if all the noise goes away.

Any resolution?
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Old 09-01-2012, 10:20 AM
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I have not done anymore work on it really. The whine is a lot less but still there with the ground strap removed. I did try a replacement ground strap and the noise came back 100%, so the noise is def coming from the engine. I looked around the engine a little and didnt see anything out of place, need to look closer.
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Old 09-01-2012, 11:26 AM
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You are confirming the irrefutable radio Law of Thirds that I discovered long ago: Radio is 1/3 science, 1/3 black art, and 1/3 dumb luck.
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Last edited by jeatock; 09-01-2012 at 11:29 AM..
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Old 09-01-2012, 11:51 AM
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Yea I'm figuring that out now... I'll probably just leave it like this for now since its just a leased vehicle.
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Old 11-04-2012, 1:49 AM
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Unhook your On STAR Antenna worked on my car.
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Old 11-04-2012, 5:41 AM
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ON my 2012 Chevy Cruze all I had to do was pull the ON STAR fuse out of the fuse block.
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Old 11-04-2012, 7:14 AM
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Quote:
Originally Posted by jluisi86 View Post
I'm really at a loss now, I checked every ground and every looks like new and is tight. I don't understand why one day everything would be fine and the next have all this noise. I would rather not put a filter on it, I would like to fix the issue. Should I try to change the alternator out?
I know this an old post but here is some food for thought. get a digital volt meter put it on the ac scale and check the voltage at the battery truck running. if you get more than .05 volts you have a bad diode in the alternator. this not uncommon in gm vehicles.

Good luck

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Old 11-04-2012, 7:26 AM
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I will have to try that with the ONSTAR antenna or fuse. 95% of the time, this problem is not around now so it doesnt bug me as much but the ONSTAR system never crossed my mind, Thanks for the tip!

I did test the alternator and it passed all the tests i could find online to do plus tests people here sent me to do. I still went out and changed the alt and it didnt fix the problem.
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Old 11-04-2012, 7:53 AM
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Radio shack use to make a noise filter that you put in line with the radio power. You might check on that as well.
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Old 11-04-2012, 8:20 AM
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Quote:
Originally Posted by morrisr3nd View Post
Radio shack use to make a noise filter that you put in line with the radio power. You might check on that as well.
It would be a good idea to get to the root of a problem than put a band aid on it.

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