I recently bought a used Fender Hot Rod Tube Amp, its in good condition but for some odd reason it makes crackling noises, it doesn't effect the tone, it just can be heard in the background, I brought it to Guitar Center and they plugged it in and it sounded fine, I bring it home and it does it again. I thought it was the cable's so I replaced them but still it makes a noise, they said maybe its my power outlet.
I assume you tried another outlet in your house?
Les Paul Traditional '08
Fender American Strat '99
Martin D16
Peavey Classic 50 2x12
535 Crybaby-Whammy-Small Clone-DD7 Delay

"I have a very high EQ--something like 3,000 hertz. If I think too hard, my brain hertz." Harrison