HP 1 with GPS kit

[principal]

I just received my Garmin GPS kit for the HP 1 and am experiencing some issues.
As soon as I plug the GPS into the HP I get :
1 - a 25% +/- reduction in output volume.
2 - a hissing white noise is introduced (constant)
3 - Snaps & crackles are accentuated
4 - Pops at the beginning & end of transmissions are added (I dont hear them without the GPS)

Any help is appreciated

 

[DaveIN]

What Garmin kit did you get? The Garmin 18x PC GPS Navigator Unit is the one I use with the XT models with no problem.

 

[principal]

Yes its the GPS 18 PC. I noticed today also that when I plugged the car charger in (the one that came with the HP 1) It causes the same symptoms... thats without the GPS in use. If both powers are plugged in, the unit becomes un-listenable.
I wonder if its a grounding issue (they are factory power outlets in the vehical)

 

[DaveIN]

Maybe you should try it in another vehicle to see if the problem continues, but it does sound like a grounding problem.

 

[principal]

Right after my last post I did try it in another car and it worked fine. Actually it works fine in the original vehicle if its not running (power ports are active when vehicle is off)
I also notice a massive EMF in the cab when the truck (Sprinter) is running... this can't be good!
Cheers - RO

 

[principal]

As it turns out, the whole problem seems to originate with the headphone jack. If I use a stereo cable from the headphone jack output, into my aux 1/4" input on my car stereo, the symptons return... so maybe a remote powered speaker is needed to achieve the volume needed at highway speeds.
Thanks for all the response's.
Cheers - RO