a few weeks ago i installed some rainbow audio componets, and they where gettin feedback, so today i went out and moved the grounding point around, sanded the paint down each time, but i am still gettin that darn feedback sound.

 

Search for engine whine threads. There have been a ton of them. You will find your answer. Manny gave the best explanation I have heard thus far. System noise usually occurs very early in the chain. Most of the time it is ground related.