u/Wado-225

Have an old Ampeg SS-140C amp that I fully recapped a little while ago. Aside from some switching JFETs in the pre-amp, everything else was solid. Fast forward to recently and it started making this weird humming noise. Never encountered this, mostly just the standard 120Hz sawtooth wave hum. The oddest part is it slowly pulses up in volume before dropping back down. Could this be a failing filter cap despite being installed less than a year ago? Or a failing transistor? Here is the schematic