This has just started happening today, my amp is making a sort of.. it's like a constant moderately quiet crackle in the background?
I've got a Marshall AVT150X,
At the moment it's set on the Clean channel, and when I turn the volume up the crackle also gets louder.

I've triedd:
* Changing guitars to see if it's the guitar that's the problem
* Changing channels to see if it's just the channel that's making the noise
* Swapped leads to see if it's the lead
* Changed plug sockets
* Turned it on and off
* Tried unplugging everything (e.g. Pedalboard) and just playing through the amp

The only thing that DID work, was when I moved the amp downstairs it was fine (or the crackle was EXTREMELY quiet).

Does anyone have any ideas?
its either the outlet u were using or there was something causing interference. is ur downstairs a basement? it could be blocking radio signals being in the basement.
Mesa F-30 - 1x12 V30
PRS SE Custom 24 (GFS Crunchy PATs)
PRS SE Singlecut (Evo/Air Norton)
1989 Starforce (GFS PowerRails)
Morley Tremonti Power Wah, TS7 (808-Mod), Pitchblack, Boss DD-3, DE FnC
I'm in the attic (loft).
I've got like a Computer and a laptop running in here most dayss.. Maybe that's the reason?

Idk, I'll have to try a few things.