When I shut down my engine, I get a ~ 5s whining noise from the rear of the car (I think...).
I am probably missing the obvious explanantion, but what is it?

My old car didn't have it.

 

Is your wife in the back seat?

 

hmmm wierd...sometimes when I shut the car off after driving it hard, the fans stay on for a little while to cool the enging. could that have been it?

 

The amplifier for the Logic 7 system has a fan that you can often hear after shutting the car off. It's mounted in the left-rear quarter panel and it is audible from outside the car.

But then again, rodneyremington may be on the right track too...

 

I've found it's pretty common for me to start whining when I turn the ignition off because I'm done driving!!

 

Those are exactly the answers I was looking for.....
Wife sits in the front and hardly ever whines - she loves BMWs

 

I've heard the whine too. I had thought it could be the electric water pump.

Tom

 

Coming from the rear?

 

I was going with the "I think" part of "coming from the rear".

 

I think I found part of it - sounds strange, but its the side bolsters of the comfort seat. But there is still another noise in the back of the car that wasn't there with my old car.