Try:

Making sure your RCA's and Power are not run on the same side...sometimes you can get away with this but not always
Regrounding your amps...make sure you have a good ground
Check your radio ground...Make sure it is also grounded properly

If you check both of those and you still have a problem then you need to buy a " Ground Loop Isolator". It goes for like $10 - $15 bucks and an audio shop. It connects between your rca cables and your amp.