It sounds like something touching the flywheel, or part of flywheel touching the housing. There is white sticker on the inner side of the flywheel used for speed sensor, if you rotate the flywheel, should see it through gap between plastic cover and the flywheel, perhaps it has delaminated and touching the housing?
The cover is held by 3 screws, if you wish to go that way and check.
Update: nothing unlodged, seems like it is coming from inside the unit. Sent it to the dealer I bought it from and got a loaner unit for now (yay!..?) . Hopefully they’ll hear from Wahoo soon and give me a solution.
I had this problem recently
Contacted Wahoo support, and they immediately sent me out a new unit under warranty.
Since they didnt ask me to go through loads of different ‘fixes’ it seems like its a known problem.
Wahoo support where very helpful though, not pleased the unit broke, but pleased with the response.