Solid state amps usually have toroidal transformers. If they buzz, I would suspect RCA interconnects, dimmer switches, flourescent lights, and maybe (maybe) the turntable motor. Start by a process of elimination. If the amp by itself (nothing attached) still buzzes, then you may have an ac wiring noise problem or the R/C shunt at the input (if there is one) has a bad cap. Of course, it is possible that the xfmr coupling to the chassis is loose, but both?. BTW, what make amp is it, and what is attached to it and how??
Buzzzzzing Transformers
My solid state monoblock transformers buzz. I use a CJ tubed preamp (PV9a) and a modified TNT Turntable. I use an SDS for motor stability and a PS audio 300 power conditioner which I set in to the very basic mode without upping the frequency. Could this conditioner be the source of the problem?