Fluctuating volume in one channel

I just noticed that the volume in the left channel was substantially lower than the right. I started switching the balance from left to right to verify this. I did this for about five minutes and I noticed the volume in the left speaker varying from slight volume to the correct volume (equal to the right speaker). Now everything is fine. This was while playing a familiar cd.

I also tried switching between mono and stereo while this was happening. I didn't have enough time to play with this to be 100% certain, but I'm ~90% certain that while in mono the levels were equal. It is hard to say, though, because the volume level in the left speaker was changing while I was playing with the balance and mono/stereo button.

Has anyone experienced this before? I have a tube CDP as well as a tube preamp. The amp is SS. Can tubes behave like this if they're going bad, or is the problem likely somewhere else?

Any help would be appreciated. Thanks.
Yes - I would see if all tubes are properly seated, especially in the pre-amp which I feel may be the culprit?

Prior to the volume issue, was there any excessive hum in the same channel?

Might want to check to see if all connections in your entire system are tight also.
Yes, check to see that all tubes are snug in place. Try rolling tubes from one side to the other, first at the amp then at the pre.
The only time I've had this was with a bad wiring connection. Jiggling the interconnects made it go away. I don't know if it was a bad contact in the interconnects or (more likely) a bad solder joint at the socket. Good luck.
When it happenned to me, I had a bad solder joint in the IC's. 2 minutes with the iron fixed it. Funny what you get when you but $2200 retail IC's here on the 'Gon for $75.
Yep had the same thing happen to me a few weeks back, change the tubes, no noise or anything from mine but when I swapped out the tubes, both channels were equal again.

Happy Listening.
I did have the same problem few years ago with my VAC pre-amp. The tubes were getting old. I exchanged the tubes (for much better sounding than the original Golden Dragon) and the problem was gone...
Good luck.
I feel better already knowing that it's probably not a major component that's damaged!

Audiobugged, no, there has never been any hum prior to this. I did notice, however, that while the phenomenon was happening today, some static was coming from the left speaker. I'm not sure if this helps determine if it's a tube, IC, or something else, but I figured I'de let you all know.

Thanks for all the help so far!