Left channel fading in and out

Actusreus,

You said you "switched the speakers". Did you literally move the L and R speakers across the room or did you swap L and R speaker cables at the amp outputs? Makes a big difference in the interpretation of your results.

Al,

I did hear crackling for a few seconds, which I immediately attributed to the problem, but it has disappeared since and I did not hear it at all yesterday when I switched the speakers. I always hear low level hiss from the tweeters with the volume know turned all the way down; perhaps the crackling was the result of some irregularity in the current that manifested itself through the speaker. I'm not sure how else to explain it. However, it is puzzling that after the switch the frequency of the fade-out seemed to have decreased, even though it was still with the same speaker.

Doug,

Yes, I physically swapped the speakers so that the right monoblock was now feeding the speaker that used to be the left one (the one revealing the problem), and vice versa. I didn't touch the cables at the amp terminals. The fade-out appeared to have moved to the right channel with the speaker. I'm in the process of contacting the dealer I bought the speakers from to see what my options are. I think they definitely need to be at least checked out.

Since the problem seems to follow the speaker, you may want to try this. Check your speakers out really well. Sometimes the drivers loosen up over time. I would check to make sure everything is tight. I don't know for sure that's the problem, but its worth a try.