Are you getting a lot of harmonics of the 120Hz?. Maybe a small value
cap like .05 across the filter caps would be worth a try.
If you redo the audio stage what about the 'modulation' of other stages?

-Bill

There is only one filter cap- 2200 uF. I'll try bypassing it.

The audio stage is the only one that gets unregulated output from the
supply. The rest of the radio is powered via a regulator.

MR