That noise is from the SMPS starting and shutting down, usually from
over current. *ANY* short on the secondary side of the SMPS will cause
this. Typical failures are secondary power supply diodes and caps, bad
HOTs, bad Flys, shorted HV splitters, shorted vert amps, shorted audio
amps. There are other causes, but these are the most common. Get a
manual and localize the load.

John