i had an interesting situation involving interference also. I would have a slight static sound/hum that was extremely noticable at low volumes or on pause etc. This became noticable after I bought and installed a new Pheonix Gold amp (which is running all brand new interior components and two 12'' subs). In my case the sound was present whether the engine was on or off. I have a brand new 2002 Jeep Grand Cherokee and installed everything myself. I didn't think it was the empeg because it worked fine in my house. After taking a pair of house speakers out to my car and hooking them up to the amp directly, there was no noise. It turns out that (at least this is my hypothesis) the wires in the door for the electrical systems for the power windows etc. were most likely causing the interference. I ran all new wiring to each of the door speakers using 12 guage wire and my problem went away. ....however, a couple of times the sound came back, it would go away if i tapped the door, or slammed it closed. Even with the speaker, in my hand out of the door, by hitting the door, the sound would come back and go away. Doesn't make much sense to me, but I haven't heard it but once since i rewired the door speakers. If you have an amp I suggest running a separate pair of speakers from it just sitting on your seat or something and see if the sound is there. Hope this helps

-george the animal steel