I would say that the manufacturer should take it back for repair. I had an amp that hummed. It drove me crazy. It is not worth the time or trouble. Tell them you want it repaired.
Why is amp toroid humming?
My 6 week old Belles 150A Hot Rod amp has started to emit a humming noise. The volume is such that it can be heard from 4-5 feet away in a dead quiet room. David Belles, the amp's designer, is being helpful and suggests that line voltage over 124v. could excite the toroid, as could line interference from rheostats, etc. However, the amp ran silent for the first six weeks and nothing has changed in the electrical system to my knowledge. Time of day/night makes no difference in presence or volume of hum. Disconnecting speaker cables or inputs makes no difference. Nor does changing power supply to a different house circuit. Anyone had experience with a problem like this?