I would try throwing in a new set of power tubes if you have spares, and if that doesn't cure it replace the 12x's one by one (or all three if you have ones you know work) IF you have spares.
If you don't have spares take it to the store you bought it from and have them retube it.
Chances are it is just the tubes, I see it sometime at the store I work at with new combos (other brands, we don't carry Budda) that just came in.. UPS jars the hell out of them
If something else is going on I would get a new amp from the dealer even if you have to wait (or a refund and get one somewhere else)
I hope this helps!