Tube Question--Slight Ringing coming from one side

I am running a pair of Klimo Monoblock amps, EL34 based. I baised them about 2 months ago, pretty much everything has remained the same except I had to move them closer together and closer to my turntable. Within the past 2 weeks, I have noticed out of the left monoblock a slight ringing (not really a ringing, but kind of like the sound of a refrigerator at idle) not at idle, but when the volume is turned up to a conversational listening level. it increases as the volume is raised

I have never experienced this before in this amp or any tube amp I've owned in 20 years. I thought of using a tube damper on the el34, but this is not addressing what may be a problem. Could it be the tubes are ageing? I was able to bias them exactly at factory specs 2 months ago.
Possibly a micophonic driver tube. Gently tap on the top of the driver tubes when it is playing and that should cause the offender to make a little more ringing. I doubt it is one of the EL34's. Not very familiar with the Klimo's
I think Dc007 is correct, although I'm not sure I'd want to be tapping on a amp driver tube unless you are an experienced tapper. :-)

What I would recommend is doing a normal process of elimination. Just switch the driver tubes from one mono to the other and see if the noise follows the tube(s). If you have more than one small tube then reverse the process one tube at a time until the noise switches back. In so doing you would also be reseating all of the driver tubes and by doing so cleaning off any accumulated corrosion.

But, what ever works......

Try swapping tubes to isolate the culprit...left > right / right > left channels on both amp and/or pre amp. Eventually, you will find the microphonic tube.

Good luck!
I'm not familiar with these amps either but, unless they are integrateds, and the noise varies with volume level, I'd suspect the preamp. If it's the preamp then it would be a tube prior to the volume control. Again, as Newbee suggested,try switching tubes from one channel to the other in the preamp one at a time until the noise switches to the other channel.
Persistent ringing is more common in small preamp & amp input tubes than in large power tubes. Flicking your fingernail (even somewhat sharply) against the tube, will usually reveal the culprit and eliminate the ringing for awhile. The juggling vibration of removing and rotating the tubes will probably also eliminate the ringing for a time. This kind of ringing is different from microphonics, and probably cannot be eliminated with damping rings.

The complaint is a description of a microphonic preamplier tube, occuring before the volume control in the signal path. The amp has nothing to do with it.
Is the Sonographe pre amp a tube unit? I thought that was a CJ solid state device? Learn something new every day.
thanks for your replies...

I had thought it was the EL34s, because I can put my ear to the tubes and hear the ringing coming from the el34s, (all of them), I am using a VTL tube preamp, and will check those tubes.

I really do not think it is mircophonics, I have experienced that before, this is not like that.

It sounds much like an old floor heater and a jingling within the heater...except it is coming from the 6 El34 tubes....
EL34s can make a 'jingly' sound that emenates directly from the tubes- in fact from the filaments.

If the output of the amplifier were shorted or open, the tubes would also make a jingly sound that would be associated with the power demands of the music they are trying to amplifiy. This is why they would get louder when you turn up the volume.

Its not a good idea to run the amplfier this way! Make sure it has a proper load.