Swing by, I can take a look at it.
I'm going to be home for the next few weeks at any rate, when I'm not at the skatepark.
I'd initially think something physical with regard to the amp, if it's reacting to bumps...
But possibly a voltage related issue as well, maybe a ground or connection somewhere that's compromised, in the power voltage path.
The music keg I'm with you... sounds like a loose connection, or a pulled wire.. and in that case, should also respond to bumps and turns?
Of course, it could be random too.. might be a hairline crack in some solder connection or something. Who knows.