Engine/AC cooling fan "Take Off" speed!

[pj8708]

When the AC is runing on my 07' S80 3.2, sometimes the engine/radiator cooling fan seems to kick in to high speed and it sounds like the engine is going to "Take Off". After a few minutes or so the fan reduces speed or at least the noise level, and settles down.
In addition, when the AC is running and you shut the engine off, the engine will stop while the cooling fan winds down sounding like a turbine spooling down.

Question. Is all of this normal? It has always done this since we've owned it, 9 months, however, the car runs like a top. Thanks.