High Pitch Noise using Direct Mixer

Hey gang, I’ve given up searching this forum; I have NEVER found a related result. My apologies if this has been covered, and please link!

I noticed in the last day a super high pitch sine wave coming from my octatrack, via the AB inputs, which are turned up in the OT mixer (dir).

Some trouble shooting I have done already;

Turn down Dir of AB - No sine wave

Fresh session on OT - Turn up Dir of AB - sine wave present

Volume down of source going to AB - sine wave present

Rerouting the source of AB to a hardware mixer - no sine wave.

The noise the octatrack is emitting is really high in pitch, and not extremely loud. I would liken it to the flyback transformers old TVs used to have (for any geezers like myself who remember that). It’s a whine… and it bugs me.

Any ideas what could be going on?

Do you by chance have USB connected from your computer to any of the devices? Source or OT?