[richtazz]

I had the same issue on my 99 GT (same 6 speaker system), and it was the rear speakers that were bad. I happened to have a set of 6x9's laying around and jumpered them in throgh the trunk to test and the problem went away. I went to Best Buy and bought a wiring kit ($6) so I didn't have to cut the factory harness and installed the speakers. Problem solved. You'll have to remove the rear seat to gain access to the speakers. Not a hard job, took me less than an hour, I could do it in 30 min now that I know what I'm doing.