You'd have to take it apart and have a look at it. It could as simple as a loose conections if it is you can fix it yourself if you can't see a loose connection leave it and take it to a Marshall dealer.

Bodacious Bob

Schecter Omen 7 Extreme
Ibanez RGR08LTD BK
Behringer TU-100
EHX Metal Muff
Boss MT-2
GLX EQ-100
Marshall VS15

Quote by tpot06
Bodacious bob wins all.