HELP!!!!Muffled Music

[SMITH23H2SUT]

O.K. Did some inspecting today, looks like the radio works fine. Amp is questionable though. Installed many systems in my younger days, and it appears that the amp is dead. Funny thing is the AMP FUSE didn't blow. RADIO and AMP fuses are good. Door chimes don't work either but after doing some research it appears all these functions are sent through the O.B.C and AMP. All the muffled sound from radio was coming from the Aftermarket Fosgate Sub System which was wired into the Radio pre-AMP. I hope I don't go out and buy an Amp just to find out that it's not the Amp. Any suggestions on what else I should check? Has this happened to any of you guys? When I get this corrected I will definitely post the answer to the problem, I'm sure this will happen to someone else and I know I'm not the only one who hates wasting time and labor trying to fix a problem and find the answer on his own. Help me out HUMMER brothers and sisters.