Most EVs (other than the Leaf) including Models S/X/3 use some form of active battery thermal management which will run pumps and fans even when the car is off and not charging, if the battery temp is out of an acceptable range. That sounds like a fan, but it sounds a bit like a fan with something stuck in it. If it continues to sound like that, I'd take it in. If it stops, maybe it just got a leaf in it.