Rockerverb 100 MKII "buzz" problem

[wrath]

So, the other day I got an used Rockerverb 100 MKII. I got it from a guy who had it for 4 years and the last two years he didn't use it at all, the amp was mostly just being kept in his rehearsal space. When we turned it on it was connected to an extension cord and it had some sort of a buzz, or a hum, or crackle, not really sure what to name it, which wasn't very loud in a sense that when you play it's very hard to notice it, especially on the dirty channel. We turned it off, disconnected it, and plugged it directly into the power socket in the wall...the "buzz" disappeared, the amp was quiet. Amp is in very good condition, everything is original including all the valves, inside everything looked mint, there was some crackling when I turned the gain knob on the dirty channel, but after a few times that I turned it up and down the crackling disappeared also. The guy said that at one point when his band was driving to a gig some cab leaned onto the amp and bent the power switch...this is so hard to notice I really had to look and touch the switch to notice it. The price was basically a steal (at least when it comes to Rockerverbs), so I decided I'll take it. When I got to my rehearsal space and turned it on the "buzz" was back...it doesn't get louder or quieter when I turn any knob. Amp is completely functional...reverb works, fx loop works, footswitches work. Other than the buzz the amp sounds great and it's of course very loud. Can wiring in the room be the cause of this? Because we don't have this kind of problems with any of our other amps...my RV50 is completely silent and my bandmate's vintage OR120 did have a bit of a hum on one of our rehearsals but it was quieter than this. I did notice, when I placed the amp on 2 4x12 cabs, from below, that one power valve seemed to glow a bit less than the others. Any thoughts?

[Les Paul Lover]

That's a difficult one.

That fact that plugged directly into the wall socket, the him disappeared seems to point out that it may not be a problem with the amp. It could be coincidental of course.

Can you take that amp somewhere else to try it out?

The tricky thing is that if your other amp behave fine in the same conditions it may have an issue with power filtering, or perhaps a preamp / fx /reverb/ power valve is going, but you'd expect that to get louder as you apply more gain / volume.

If you power up the amp for a while (say 1 hour or more) is the problem the same?

[wrath]

That's a difficult one.

That fact that plugged directly into the wall socket, the him disappeared seems to point out that it may not be a problem with the amp. It could be coincidental of course.

Can you take that amp somewhere else to try it out?

The tricky thing is that if your other amp behave fine in the same conditions it may have an issue with power filtering, or perhaps a preamp / fx /reverb/ power valve is going, but you'd expect that to get louder as you apply more gain / volume.

If you power up the amp for a while (say 1 hour or more) is the problem the same?

I haven't had a chance to play it for a longer period of time yet, cuz I just dropped it off at the rehearsal room that day, plugged it in, played it or like half an hour, tried to figure things out on my own. Tomorrow I'm to my tech to pick up that OR he restored and will ask him, then I'm going to rehearsal space to try both amps out a bit more...I'll play it longer and see. Yeah I can try it in another rehearsal space where my other band is but this is the heaviest amp I ever lifted (the only heavier was one 200 watt Hiwatt clone) and I'm totally not in the mood for hauling it around now.
Unfortunately I don't have any cabs at home.