Low Decible Feedback

I've hooked up my whole system as proper as i can. all the wires are separate. the amps power lines on the opposite side of car from the audio cables. everything's wired right. but theres a low and VERY annoying thumping coming through the speakers and the bass. i think its coming from the alternator because when i rev the engine it gets louder and and faster. my friend who knows a little about sound systems believes that the problem can be solved with either hooking up a second battery for the amps or putting in a power cap. i've been looking at princing for power caps and i think i'll go with one of them. but i want to know if there is anything i should check first before i buy one. does anyone know if there are any other reasons why it is making this annoying thumping noise.

a cap will NOT fix this problem.

Turn the stereo off, unplug the rca's from the sub amp only. Turn the stereo back on and see if the noise is still there with the car started. Let me kbnow how that turns out.

I've done this many times. the amps don't seem to be what are causing the problems. and my friend listened to the sound and said it was the same thing he had until he put in a power cap. and his logic seemed pretty sound.

werll, I can't really help you if you just want to go from one solution to the next without actually troubleshooting it. I doubt the cap will help but stranger things have happened,

well i'm not going from one solution to the next without troubleshooting.... as i asked. what else might cause this weird problem... you suggested the sub amp... i've checked it... my friend suggested power cap. i don't want that until im sure i need it and theres no way i can test that... would it help if i made an audio recording of the sound

troubleshooting means narrowing the problem down, if you unplug the RCA's to the sub amp you will be able to tell which side of the circuit the problem is coming from.