After 3,000 miles of silence my chirps have returned. Very faint in the car with the windows up and the stereo off, wouldn't notice with the stereo on, haven't bothered opening the hood.
Only change is I did drive up to 6,000+ ft above sea level from my regular altitude of ~10 ft.
All 91 octane E10 at the most convenient station, original pump, ~13k miles, 12/12 build. Will update according to changes.
:happy0180:
Edit: just took my friend for a ride, he doesn't hear it, he thinks I'm paranoid
opened the hood and everything.