M925A1 Beeping?

Finally got my new toy home (all is good) but it's letting out a quiet beep about every minute or so when it's completely powered down. My old 923a1 was doing the same and I found the PCB bypassed - once I replaced it, the sound went away.

Unless it's bypassed in a way that's not obvious, this unit's PCB seems ok.

I don't want to ignore it in case its a battery drain.

-Anybody ran into this before?

The main battery switch is off when it does this?
I've never heard of this before. Did a previous owner add some aftermarket gizmo that is tucked away somewhere?

The beeps sound as if a short pulse is being sent to the parking brake buzzer. I recently replaced all my batteries and cabling, so my initial thought was incorrect connections. I’ve double checked everything - it’s not that.

I've had my PCB disconnected for a few days (which stopped the beeping). I reconnected it today, and the beeping did not return. I'm assuming I have a weak contactor in the PCB (guessing).

Thanks

Or a switch that isn't cutting the power off completely Could be either one with an intermittent issue