I have similar sounds especially after disconnecting from a SuperCharger. Sounds like the AC turning on to cool the battery.Here's the video. . .
This is normal. My car does it and I asked the same thing. Its just a fan sound from 2 things. Whenever you open your door the AC will usually turn on and when you come back from a drive it will have that sound for sometimes a long time after. Mine sometimes does it for like an hour after driving. That is the battery cooling system or your AC preventing your car from getting that bad smell that most 3s get. hope this helps!