[bmw] E36 stock stereo problem/question

[Brendon <brendonm@xxxxxxxxxxxxxx>]

Folks:

I have the stock Alpine CD changer, headunit (radio) and amplifier in my '96 328 sedan.

Lately I've noticed that when I go over a big bump, the sound will disappear/lower
on the driver side.  Then I hit another bump and presto -- the sound is back/fuller.

My mechanic told me I could have dirt on the on/off nob on the headunit, but I don't think that's it.
I checked the wire harnesses that connect to the amp in the trunk and they seem to be
securely connected to the amp.  

What could be causing this loss and then gain of sound? Could one of the wire harnesses or even the connectors on the amp or the amp itself simply be  going bad?  I haven't rulled out a bad connection to the speakers in the driver's side door either.

While I'm on this subject:  Can the stock amp be replaced by other aftermarket amps?  If so, can
anyone recommend one?   Or do I need special wire harness adapter from someone like Crutchfield to do this?

TIA,
-Brendon
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