[Amps] Strange relay problem Alpha 76

[Carl]

Ive not seen this failure mode before and wonder what causes it.

The Power On relay is a simple DPST 120VAC job. It all of a sudden 
started buzzing with the amp in standby.

Pulled the coil leads off and hot wired and it still buzzes.

Fired off the DC supply and it works just fine on 120VDC now, no 
overheating.

What gives? I understand the construction difference between AC and DC 
relays, coil impedance, etc.

Carl
KM1H