@jellotherat:
Thanks for the info. I've done a bit of searching and found one at crutchfield that I might end up buying. I'm going to do a bit of research since, from what I've seen at least, it sounds like the ground loop isolator will get rid of the slight buzz, but might not get rid of the thumping/pulsing sound.

I'll be trying a ferrite "choke" tomorrow, but it will probably be quite a while before I try something more expensive. I'll update the thread with any new info.

Thanks for the help.