Hi, I'm having weird and terrible trouble with a Bassman 100 when i turn the amp on - without any input going in, by that i mean no bass lead or effects etc - it honks, i can see the speaker cone has no damage. i've put on the mute switch, turned the mids, trebles, bass, gain and volume off/on but it still honks...i have no idea why. anyone else ever have trouble like that? any idea what the solution might be? before i haul it into the shop for help...cos i've got 3 gigs in the next 2 weeks, if i can fix it myself i'd prefer to.