Looks like it was off axis CO because all whistlers have a distinctive pulse I/O audio detection feature.
It is one of the best I/O detectors btw.
Just wish my 78 SE performance wasn't so spotty. I had a few similar experiences with the brand.
Whislter Radar Detecter Failing - YouTube
Glad the officer was being very generous this day.
and that I wasn't speeding when mine happened