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Figured out my problem. The crappy amps I bought from acaraudio both had problems, so I sent them back and got new ones. What happened, was that one of the crappy amps blew out my head unit's rca ground. What I did was I wrapped a wire around the outside of one of the headunit's rca outs, and the other end of the wire went to the headunit's ground. The engine noise instantly went away!

That is why it is called a 'ground loup' isolation problem. :) The poor ground may exist in either source but you wouldn't expect to have the problem with a portable device because it does not share it's power supply with your amp. Check to see where your amp is grounded, what size ground and power cables were used (should be the same pos and neg gauge), and the length of your ground cable. That will help diagnose the problem (maybe).

Head unit ground, or amp ground? Like I said, if I hook up my portable straight to the amp, there is no noise w/ the car running.

There have been a few posts on here lately about engine noise/ground loop isolating. Check in the FAQ section for specifics, but you most likely have a bad ground. That is what typically produces engine noise through the audio system.

I have an 02 TL. I had a complete system professionally installed, including a deck, 4 speakers, 2 subs, 4 ch amp, and 2ch amp. Originally, I had the 2 fronts hooked up to the 4 channel for about a week (didnt have time to do the rears or subs). No engine noise, and it sounded great. The audio shop later added the rears and hooked them up. The amp blew a minute later (bad amp), so they offered to put the sub amp on them temporarily. Once the sub amp was hooked up, I had instant engine noise. Now I have ordered a new 4 channel, just hooked it up, and it has engine noise with a turn on pop! All rcas have it, and if I plug in my portable mp3 player with rcas there is no noise. What could the installer have done? Remember, I had no noise originally.