[RMG]

Picking up my car from the hands of the BMW Service in Sudbury MA yesterday ( it was a simple coolant flush and oil change+ battery cable recall ) went from a horrible experience (the front bumper scratched, the engine mysteriously showing "MAX" when I left in the trunk only 6 quarts of oil) to a nightmare... just before getting home when I've noticed a weird drone noise coming from the engine (on the exhaust side). Please find attached here a video - video taken with my iPhone - for conformity. The drone noise coming from the exhaust side of the engine - that subsides around 0:22 into the video - came back again this morning when I started the car but was less intense.
Can anyone recognize this sound?
Many thanks!