ARGGHH its back (alternator whine)
 

The dreaded high pitch alternator whine when using the aux stereo jack is back.
I used a plug in filter and it mostly elminated the problem. For some reason it returned. When the RPMs go up the whine gets louder. I took it to a sound shop and they didn' know what to do. Made another pit stop and they tried a different filter. On a test ride the whine was gone. Pay the shop (they were closing) get in drive home and.....same as before. They're closed today. :(

If anyone has figured out a way to completely get rid of this short of just replacing the whole head unit and not dealing with aux please shed some light.
It sucks!!!

Check your connections. When I had an OEM amp converter (dont really remember, just remember crutchfield said i needed it, small black box in between the head unit and the stock amp) for my head unit it would whine until i hit it with my foot to shift the connections. It may be internal so it would be hard to find. Easiest way to find out is buy a head unit form walmart, install it, and if the whine is gone thats your problem, if not just return it.