Whenever you've got more than one DC component in the car audio system (i.e., more than one separate amp, a separate crossover, etc.), you have the opportunity for ground loops. And I've seen some nasty ground loops that will enhance and amplify the alternator whine. So, as your subject line suggested, you could be dealing with two separate issues here that sound like they're part of the same issue.

Issue 1: Ground loops between multiple components.

Ah, the black magic of 12-volt audio. I'm only just beginning to learn the proper spells and incantations (eye of newt/wing of bat/8-gauge cable/filter that/boil bubble/toil and trouble/run twisted pair/and ground it double).

As I understand ground loops, the idea is as follows: You've got an amp hooked up to the car chassis with X potential to ground. You've got a head unit hooked up with X potential to ground. You've got another amp with X potential to ground. Etc.

All of those X's are going to be slightly different values. And when that happens, power voltage gets carried through the audio circuitry towards the unit with the best ground, causing noise. This isn't always up to you, either, some equipment will have different potentials internal to their circuitry (grrr, I just found this out, one of my amps is this way. Gonna have to ditch it someday).

This gets complicated by the fact that some components have two grounds: The chassis and the ground wire, and sometimes those have two different potentials.

To remove bad ground loops, you might have to insulate every single one of your components from the car chassis (right down to taping the Empeg docking sleeve if necessary), and run all the power and ground wires to the same point using heavy-gauge wire. This is, as you've said, usually very logistically difficult.

Also, check your amps for ground-loop defeater switches/connectors. For instance, some amps have a little switch or connector which changes its ground potential to help resolve ground loop issues. Some amps have two separate grounding screws that you can switch between.

Issue 2: Alternator whine.

Even when you get rid of all ground loops, you can still have some alternator whine on the primary power lead (although the fewer grounding problems, the less noisy this will be).

Even though the Empeg has a small noise filter on it, you might need to noise filter the amps themselves. That's what I've done: I got the heaviest-duty noise filter that Radio Shack makes (20 amps) and put it on my main power lead that I ran from the battery. Everything powers off of that lead after the noise filter. Depending on your amps, you might need to split your power and run multiple noise filters to different amps.

It varies from car to car. I didn't need to do all that on my VW, it only became necessary on my Honda. Probably because of all the additional electronic equipment in that Honda.

There's also the possibility of induced noise in your audio/speaker cable runs. Run some loose RCA cables out away from the other wiring and see if some of the noise is being picked up RF-style from unfiltered wiring running along your floor tunnels.

Finally, you'll want to make sure your amp gains are adjusted down to reasonable levels. Ground loop noise and alternator whine are always present in every car, the only question is to what degree they are present. Even a perfect system has a noise floor, and if you crank your amps up, you will be able to hear that noise floor no matter what. Set your amps so that 0db on the head unit is the loudest you'll want the amps to play during normal listening.

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Tony Fabris