There seems to be a supplemental motor driving a fan for these seats. When I first got the car i wondered why there was a rushing sound that would not go away... then I discovered one of the seat heaters was turned on. If found that surprising because my old car would just heat the seats silently, probably using wires stitched into the seat.

i don't know for sure, but if you hear a buzz... maybe some dirt or debris got into the fan somehow. Not sure how easy it is to get inside that and take a look