I noticed this a few days ago. When i plug in my 2525H head and run the overdrive channel, there is a very strong loud (sounds like) electrical noise. It goes away when i remove the pedals hooked up into the loop.
Now i run a couple of EQ's, mxr 10band eqs on 18v power and a DD7 delay pedal in the loop. I have checked each pedal individually and also changed the cables used and it doesnt go away.
I also checked if its a power supply issue, i run a t rex fuel tank chameleon that powers all my pedals, the 18v jack i have used a daisy chain to hook up 3 pedals, a Fulltone OCD, and the 2 eq pedals, i checked the power draw on each and it is wayy within the required power that is given out of that 18v socket.
Please help, this is recent, i never had this problem before. I've gigged with this amp on a few occassions too, noithing was noticeable, and with this issue its very noticeable on low volumes as well.
If you could try connecting just a patch lead with no effects between the send and return on the amplifier and see if the noise is present, if the amplifier is silent when using just the patch lead this may suggest one of the pedals is causing the noise. If the noise is still present we would recommend that you have it looked at by an engineer or contact your dealer.