Thanks.
I had my OD channel input jacks wired like this:
Having seen a different layout for the (blue w/ white stripe) ground run from the normal channel's volume pot, I moved it like so:
That got rid of the hum, but now the amp is acting pretty crazy - if I plug into the "hi" jack of the OD channel everything seems to work OK, but if I move the plug to the "lo" jack, volume drops off to a very low level for the knob setting, and if I turn it up halfway and start feeding signal (like hard-strummed chords) all of a sudden it will kick in to normal volume with one of the strums, scaring the crap out of me and probably jolting the speakers a bit.
Then, when I move the plug back to the "hi" jack, instead of working normally the volume is extremely low again, pulling the same scare-the-crap-out-of-me maneuver when I start playing (it will leap back to normal volume on the 8th or 9th chord, for instance). And I'm having similar issues now with the inputs fopr the normal channel.
I suppose, then, that I should move that run back to where it was?
Any other suggestions?