Acoustically rather than electronically.

I've had my A&H GS3 down for about 9 months, and after cleaning it and
replacing some faders I hooked it up to test it before installing it.

The power supply always made a small bit of hum/buzz, but it seems to
be a lot more than I remember.

There is no hum/buzz in the actual audio, but the PS itself is making
a fair amount of hum acoustically by itself.

It's the original PS, the console was built in December of 1992.

Any thoughts on what to replace, look at, etc.?

I've got a service manual but it doesn't really talk much about the
power supply.

FWIW the model number of the PS is MPS9.

My A&H System 8 has a slighter smaller PS (model number MPS8) that
does not make nearly as much buzz, and that PS dates from 1988.

Analogeezer