bizarre noise with RM50

[boogie1]

Hello all
I have a small issue that maybe someone here can help with. I have an RM50, blackface module, mr scary, and ultra xl. The amp sounds great. But there is this crazy electronic whirring noise that is present when I turn the guitar volume all the way down, and as I gradually turn the volume up, the frequency changes. It is not really noticeable when playing at volume, but it is really annoying when turned down. The sound isn't horribly loud, but it definitely isn't normal tube amp noise.

I have switched every tube (one at a time , then the whole bunch) no change. changed cables, changed guitar, changed power cords. lifted ground. It is present on dirty and clean, more so on dirty of course. I did the capacitor on the input jack fix for radio stations.
It sounds like a shortwave radio almost (but a constant frequency with guitar volume at zero). And sometimes when I turn the guitar all the way down fast. the sound comes in quickly like a reverse hush unit. Could the fan be causing a hum like that (the more I think about it, the more that sounds likely) but I wanted to check with the folks here first
Is there anything else I can try before I take it to my tech

Thank you so much for your time
Lee

 

[Julia]

Does it sound like a cooling fan?

 

[boogie1]

Julia
It is hard to describe it other than an electronic whirring sound coming through the speakers. Does the fan on these transfer noise to the system sometimes.
It is a constant sound tho. would it hurt the unit to disconnect the fan for a bit to see if that is the problem.

Thanks
Lee

 

[Mister Joshua]

You can disconnect the fan for a short while with no problem. I'd not run it more than 10 minutes or so sans fan. Also check grounds. A loose or missing ground can allow all sorts of silly noise through.

Peace, Joshua

 

[boogie1]

First I would like to thank you for the help

Okay..here is what I found, it is not the fan. The capacitor on the input jack stopped the noise except for when using the mr. scary module. I was so busy hearing the squeal that I was hearing it in my sleep apparently.
Now here is an odd thing I have around ten JJ 12ax7 tubes that I know are good. If I place ANY 12ax7 other than a JJ in the (looking from the rear of the module) left tube socket, weird noise goes away. A electro harmonix there sounds best, a tesla does not have as much oomph. If I switch them and place the EH in the right and a JJ in the left, It sounds like Moscow trying to radio in. switch them back and wonderful tone.
Have you ever heard of something like this.
I own quite a few tube amps, and I know different tubes in different sockets can have a major effect on tone, and every amp is its own thing. But frequency hum?
Is this someting I should send out to be fixed or is it just a quircky tube thing with this particular module.
Thanks guys