No, definitely it is not from the suspension. My X5 does not have self-level suspension and I still have the weird noise.
I stay in my locked car and realise the noise comes for every 20 or 30 minutes.

You can try this: park your car but do not turn off the engine, now you turn off the air conditioner, (not only the compressor but also the fan),
you will hear the noise immediately.

So I believe it's kind of noise from ventilation system.

perhaps it's the flaps for the auto air recirculation returning to closed when exiting the vehicle and the reopening on unlock.

I think so, too. :iagree:

But if you stay in or close to your car for longer time, you will find the noise comes for every 20 ~30 minutes. Not only happen when locking or unlocking the door.

I have no key-less or comfort access and I ever stay in my car for more than 1 hour, I keep on hearing the noise.

Does she breath? :rofl:

Maybe we are hearing different things. This noise I hear is much too loud to be that, and it comes from towards the back of the car from what I could ascertain.

I believe it is the soft close for the hatch activating for whatever reason.. It's the same sound...

Mike

....its alive.... :)

I notice this sound on my 2007 X5 4.8i, but I ALSO noticed this sound on a 5-series loaner I had today. When I hit the unlock doors button, I heard the same hiss for a second or two. So it's not an X5 thing.

I agree. I remember a similiar sound in my previous E46, it was the fuel pump getting ready for start-up.

Thats what I think it is too. im not sure. I know its not the suspension because my E60 has the same exact noise.

perhaps its farting