It started in the front pass. door speaker, so i thought it was blown. then it started coming from both back speakers. i left the radio off for a couple days, then it was gone, systen sounds fine. is it a wiring issue you think? now i'm starting to hear it a little bit again. '04 6cyl

 

I have a 96 stang and i had similar problem with my speakers. Do you have an aftermarket head unit? If so i have an aftermarket head unit/stereo and i had same problem what i found out was that whoever installed it didnt bypass the factory amp so it caused the clicking noise that i was hearing. also if u remove door panel the plastic liner on the door causes a distortion noise such as clicking. i removed it and lined the door with the dynamat door kit and it solved the problem. hope this will help.