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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