Video of hum noise when I switch on the reverb of my Twin Amp

[mouton]

Hi,

Here is a video of me switching on and off the reverb of my Twin Amp:

YouTube - twin amp.wmv

The hum gets louder when I turn up the reverb. In my video, the reverb was at 6 (of 10 graduations) and all volume at 0. The hum remains the same if I disconnect the footswitch and with everything unplugged from the amp (no guitar, nothing).

The amp is only 4 years old and in very good condition, tubes are new and correctly biased, apart from the noise the reverb is working normally.

I checked the reverb cables and they are ok.

I should add that the tremolo is producing the same kind of hum with the modulation on top of it.

Do you experience the same problem?

Thank you.