Audible Illusions Tube Pre-Amp Hum- Help Diagnosing

Began getting a low-level hum from the pre-amp which stays at the same low volume no matter where volume pots are set.  Both channels are affected, although it seems to have begun in one channel (or maybe it had been more noticable in one channel, or maybe it was my imagination.)

Is this a tube thing, a ground thing, or some other issue?  

Would like to narrow down possibilities before tearing apart the installation and/or buying tubes or other things unnecessarily. 

Thanks in advance for any guidance.
A 'tube thing' would more likely be a static like noise and it would more likely appear in one channel (at least first). I would focus on a 'ground thing' and start disconnecting your sources, one at a time an see if it goes away. If not then disconnect your amp from your preamp and see what happens. Don't forget to turn off your amp when making these connections!
Thanks, Newbee. The one thing that is throwing my thinking off is that the hum (noise?) doesn't increase in volume, which is something I would otherwise expect to happen with a ground issue(?)  The problem seemed to have begun on one channel, though, so maybe a tube issue is still a possibility?  

I hadn't thought to disconnect sources one at a time as you suggested.  Will try that first.  
You are right re tube noise being static and ground hums being varible depending on volume setting. I was just trying to simplify. If you have them on hand, it is more simple to change out the small tubes and see what happens.
Mute the unit
 If it still hums let me know
Move the outboard power supply away.
Move the unit farther away from what is under it or above it.
Try 2 new shielded cables from pre amp to Power amp
If you have Cable tv disconnect the feed from the cable box to the pre
 if it goes away you need a Transformer on the cable coax in line.
 Best JohnnyR 
I have a C-J that uses a 6922 tube.   I had the same symptom.  Replaced tube and it was quiet again.  Used Gold Lion 6922, excellent tube.  
Not sure whether this thread would still be seen. I have the same issue and if I mute the unit, the hum/hiss/buzz goes away. It is more of a static sound. I am going to try to take the tubes out and clean the socket with deoxit and see if that solves it.
(((It is more of a static sound. I am going to try to take the tubes out and clean the socket with deoxit and see if that solves it.)))

Don't gum up things inside there.
 unplug the unit from AC
 Just use compressed air.
 install a new set of 6 H 23 tubes if
you are still getting static after that install a better pair of shielded cables.
  Dont forget this unit inverts polarity swap both speaker wires at speakers.
Best JohnnyR
Does anybody care which model A I this is, its age, or how/where it was purchased from?

Tubes, cables, cleaning???!!!   Really?

Your attenuators are toast. A I insists they have a life span.

Questions for the A I experts here who've actually had this work done:
How much does A I currently charge for an attenuator assembly replacement?
How long does A I usually take to have this work done? 

Get rid of it like your hair's on fire because their next question will be, "wouldn't you like us to upgrade the entire unit for just $xxxx?
Yes?  "Oh just send us the check with your unit" 

Most other equally fine preamplifiers offer a single volume that will last a lifetime and can be set at ANY desired level you hear not by having to look at the dots on the knobs and a transformer that doesn't hum. 

Honestly jumbo, I really hope I'm wrong.