Weird behaviour from Bose system

[screedchan]

My 94 E420 has the Bose system installed, along with the integrated cell phone. Occasionally, the volume on the stereo will perceptibly change so that the right channel is louder than the left. This happens even though I do not touch the volume control. It does not seem dependent on engine speed. It happens quite rarely, and without any real warning. I simply do not know what triggers it.

I do not plan on doing anything about it until it becomes more acute, but I am curious what could be causing the problem. I think these Bose systems have separate amplifiers for each speaker, so I guess that maybe the left front amp(s) is getting a little glitchy. I would hope that the head unit is not the problem.