Well, my poor 5150 seems to be having a problem. It works fine for a while, but all of a sudden, without warning, it stops its normal operation and starts making this deafening hum (sounds like a ground loop cranked to 11 or something). I immediately turn off the amp, wait a little while, and then turn it back on, and it works fine for a while, and then does it again. I tried switching out all the tubes, and that doesn't help at all. Has anyone else run into this, or does anyone have any ideas what it might be? It's kind of hard to record when it blasts you with hum with no warning, not to mention the fact that it scares the shit out of me every time it does it. Also, I don't want to ruin the amp by continuing to use it if this problem might damage it further.