Alright so here is the problem. I have the stock HU and stock everything audio, well I also have a Zune (mp3 player) and when I plug the car power cord into the cig lighters I get this ____ty buzzing, high picthed squeel and it goes based on my rpm. Like the higher rpm the louder the squeel. When i unplug the power cord and just run off of the device battery it goes away. Any suggestions on what might be the cause and what i could do to fix it?

 

you need to get a ground loop isolator.... you're getting feedback from the alternator.. which is where the rpm and related buzzing comes from