I'm not sure if this is the right forum to ask about this, but I have a little problem with this amp. I use an Ibanez SR405-QM bass, which uses active pickups, and when I play at louder volumes on the amp, I get a distortion that makes it impossible to play on the amp at all. It's not clipping, just getting a nasty buzz. Is there any way I can get rid of this distortion while still being able to play loudly through the amp?
Check the amp to make sure there aren't any parts vibrating. Check the grill, tighten the screws on the cabinet and speakers if they are loose, etc.. If that doesn't help, try lowering the volume on the bass and using the volume knob on the amp more.
I've had problems like this before too, although with different amps/basses. The solutions I found were to tighten the screws around the speaker cone itself, and to make sure it's not clipping.
I love my Bassman, but the horn is very noisy. I would turn down the horn down and see if that makes things better.