OK this has got me stumped. I have no sound coming from the four speakers. I have power to the head unit and is functioning properly i.e. tracks are running etc. The speakers and head unit are aftermarket. There is no external amp. The system was running fine for months when one day nothing coming from the speakers. When I turn on the head unit I hear a pop sound from the speakers. NOTE: the original system was non-Bose. Things I have done to test the system. 1. Swapped out head unit with aspare and had same result. 2. Checked speaker harness etc. and all are OK. 3. Checked both Audio 1 (20 amp) and Audio 2 (10 amp) fuses and are OK. 4. Checked fuse banks for continuity and are OK. 5. Reset head unit to factory spec. Weird thing is the stereo will power up and run with the 20 amp fuse pulled. Has anyone come across this before. I have searched threads, forums etc. and found nothing. Any help would be appreciated.