You are just a wealth of information. After taking all of that into consideration, this is all I can say:

I doubt it is the fault of either the alternator or the battery, as both are brand new; recently installed and tested by my mechanic, whom I trust.

I'm not sure what to think about a supression capacitor, as I've never seen or heard of it before new and so don't know how it's used. And as for the power line noise filter, is it possible that there is so much noise that the empeg's isn't enough?

But anyway, I've decided to put this on hold. The noise isn't audbile until high volume levels, and I find that cleaner sound is important to me. So I will not turn it up very loud if the sound gets too dirty. So this problem will wait until I put in my amplifier, which should be soon. Hopefully.

Thanks everyone for help and suggestions. I will keep this thread in My Favorites so that I can use it later in order to nail down the ground loop when I do the amp install.