If you have access to the remote amp line, try disconnecting it when the noise starts and then reconnect it. This would effectively "reboot" (really power cycle) the amp. It would at least prove/disprove the theory mentioned.

If the amp is accessible and is fused itself, you could try removing/replacing the fuse. I'd be a little more wary of doing this though. It might generate a nasty speaker thump.
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Christian
#40104192 120Gb (no longer in my E36 M3, won't fit the E46 M3)