I am having a Hum problem with my SVT Classic. It makes a hum with nothing plugged into the input, It gets louder when you turn the gain up and the eq changes the hum too. Is there a way a user can determine if this is a bad solder connection to the ground on the input jack or do I need to take it to a service technician to see weather this is a bad filter cap or input grounding problem. has anyone else experienced this problem with an SVT Classic? If so what did you do to isolate the problem or determine what was wrong? Amp has been used about once a month for the past few years.