HT-20R MKII Strange Chirping/Buzzing Noise

[BNuggsAW]

I posted this in the HT Series forum a while ago but that forum seems to be dead, so I'll post here as well.

I have had this HT-20R MKII for several months now and have had this intermittent issue with it from the start. It may go several days or weeks without occurring, seemingly at random.

The noise in question is a harsh electrical/chirping noise that starts, lasts for about 15-30 seconds, and then stops.

Here is an example I managed to catch on video: https://youtube.com/shorts/iqE8cydqNQw.

This happens no matter where in the house I have it plugged in. Another oddity with it is the chirping has whatever effects pedal I have activated applied to it as well, but will also happen if nothing but the input cable is plugged in (I have tried switching cables to no avail).

I have tried everything short of getting some sort of clean power supply or power conditioner for it and swapping in new tubes.

Any help would be appreciated.