The Mysterious Dropping and Migrating Channel

Have any of you ever experienced a channel all of a sudden become "staticy" or weak, or just drop-out completely so one speaker is completely silent? The strange thing about this problem is that it comes and go. Both channels will work fine, and then the problem will start. Even stranger is that without swapping cables, the problem can sometimes affect the right side or the left side, but never both channels.

When one side is afflicted, I have swapped RCA cables and the problem immediately affects the other side. I've concluded therefore that the problem must reside in the pre-amp.

My system is Accuphase (P-600 amp and C-280 preamp) driving Snell Acoustic IIIA speakers. This happens regardless of audio source and never seems to affect both channels at once.

Has anyone heard of this problem? Am I correct in assuming the pre-amp? I'm new to high audio and would greatly appreciate your feedback and gut feelings before I send this in to Accuphase's sole North American tech support center.

Thank you!