Quick Question about wiring??

first check your amplifier grounds. that happened to me in my jeep, and it turned out that where i grounded my amp, tehre was some kidn of rubber-ish adhesive under it. make sure the groudn point is clean, bare metal.

Like Saleen said, check your grounds, as that's what it usually is. If that doesn't help, you might make sure that your RCAs aren't running too close to the power wire, as that can also induce some noise sometimes. The bare metal thing is pretty essential for the grounding point. Sand off some paint if you have to.

Sounds like a ground loop. This can be the result of several things. Poor ground, week or poor alternator dioads, other vehicle electronics. Have your amp power wire running to the amp on one side of the vehicle and your rca's running back to the amp on the other side. Find an isolated ground. Grounding the amp should be the only thing that this bolt, lockwasher and nut are for. Don't ground it to a seat bolt or near another piece of the vehicles electronics. ie. fuel pump, conv. motor. Best results are when the amp is grounded as close to itself as possible or 18 inches or less. If you have to drill a hole. Look before drilling of course.Go to your local car audio store or walmart and get a ground loop isolator. This goes between your head unit and the amp on the rca's. It will eliminate all or almost all alternator whine and noise. Their is also a noise filter that connects between your head unit's power and ground wires to the vehicles factory wiring. You just splice it inbetween the wires. These things will greatly help with or get rid of all your unwanted noise.

i had one of my RCA's get smushed under the carpet somewhow. i'd check all your RCA's too

gatzer sounds like he knows what he is talking about. But, before you try the filter route, I suggest you extend the ground from the head unit to the amp's ground. This will eliminate the ground loop between the head unit and amp. Try it, it's cheaper than a filter and only takes a couple of feet of wire.