Recently my music started to cut off and on, off and on, and then just ceased to play altogether. Let me back up some...i have a 2-channel amp running my car speakers (no subs at the moment). I have a capacitor tied to that amp. with car off and key in ignition, it reads around 12V, as it should. but when i start the car, the voltage on the cap varies between 9 and 11 Volts, causing the amp to not have enough power to play my beloved Tupac. took my car to advanced Auto and got the alternator and battery checked - they're both working fine. what could the problem be?