High Pitched Sound While Driving

[CA Dreamin]

My 2017 650i GC makes a high pitched sound that happens periodically (maybe once or twice a month) and doesn't go away until the engine is off. I was able to catch it on video - hoping someone else has any ideas. I've taken it to the dealer and there are no codes and it doesn't happen on demand - so they're at a loss. Has anyone else had this issue or know what to look for?

Also, the AC and radio are off and the car is usually in comfort or economy dive modes. Also the car has been warmed up - usually running hard at least 45 min. Any help or ideas are much appreciated (see attached video & audio).