PS-2 hum on Operate

Date and place of purchase (if purchased new) - ~4 years ago, purchased directly from Fryette.com.

A complete description of your issue including other gear you use together with the product.
a while back my PS started making a hum when switched from standby to operate. it started one day and has not wavered. i’ve been living with it for several months and the unit works great otherwise. the hum is not affected by any input or output volume. i have tested and swapped the tubes to no avail.

i have 4 heads (soldano HR avenger 50, fryette deliverance 60 series II, marshall sv20h, and a mojotone 1-watt kit) and a single 412 cabinet. i use the PS to enjoy these amps at family-friendly volumes. the PS has been an absolute lifesaver as it allows all these heads to lean on the PS effects loops, minimizing the cable swapping when i switch heads (i only have to switch the speaker cable).

i have never used the line out or recording features, and the PS has never left its perch atop my cabinet.

please help! i’ve built amps and pedals and guitars and i’m not afraid to replace components if there’s a known, easy fix.

thank you for any and all. i love the PS – it’s the single most useful piece of gear i’ve ever owned.