It's been a few years now since I played this amp. It's been stored at room tempature the whole time. Anyway I go to plug in, and it's hissing and poping like crazy. Ever accidentally pull the quarter jack out of your bass while it's still plugged in to the amp? I'm getting that sound too - before even plugging in too! If I crank it up I get a lot of popping and clipping, with the tone spiking up and down in volume and lots of popping. I've tried different basses and different cables, no change. Any diagnosis?