So a friend of mine who installs sound systems into cars put my speakers in. they sound good sometimes and other times one or both will fade. this is usualy fixed by smacking the door. i took the door panel off to look at it and everything looked good, all the connections looked good. one of the speakers doesnt make any sound now and smacking or openning and shutting the door isn't helping. any idea what's wrong with my system? thanks a lot guys. ur input is appreciated.

 

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sounds like a loose connection somewhere, if hitting it makes it work sometimes, then you were jarring it enough to make the connection "good enough" to work for a little while...

I'd tell your friend that it's not connected very well, and ask him to fix it.