I'll be damned, Well at least you got a free ring modulator out of it. You don't change anything with your signal path or I/O in Reaper, and the problem disappears after closing and restarting Reaper? Obviously this Ring modulation does stay on the recorded tracks though yea...Never happened before, you don't have any batteries in your recording signal path, never pickup any interference in the axe? I will be interested when this mystery is solved