I own a Roland VGA-7 modeling guitar amplifier,
which I purchased 4 years ago.Recently it has begun to
generate an unusual crackling noise by itself after
it is turned on, as if there were some sort of ground
interference between the internal signal paths.
I attempted to reconnect the power cable to another
receptacle, readjusted the input jack bolts,
and blasted some canned air inside the input jacks,
but nothing provided any results and the noise persisted.
What source would be causing this interference?

Music - Roland