Where in the circuit is the buzz coming from? - does turning down the Loop Active Master stop it? Or the channel master? Or the gain? Is it a constant-frequency buzz (eg 120Hz) or something more random?
If it's a problem with the amp it could be a tube, a bad ground or a failing filter cap, but if the other amps buzz too it may be some sort of basic problem with your playing environment that the Tremoverb is just a bit more sensitive to.
