@alvin1118 might have some thoughts.
To check on @mahler123 's theory, have no noticed if the OS/non-OS light is changing status?
FWIW, I run a Pontus and an opticalRendu, but haven't had your issue, even though I'm in TX in a spot with notoriously wonky electrical grid. When running analog, I find voltage fluctuations lead me to regularly fine tuning the spped read by the tachometer on my turntable. Cheers,
Spencer