X5 30i making air release noise when starting

[adrezs69]

Hi,
If I don't start the car for a few days, when I first start the car in the morning or anytime during the day after a day or so rest.
When I start it there sounds like a release of air or vacuum sound comes from in the engine area.
Very hard to pinpoint because it does not do it all of the time.
Spoke to the mechanic and he said I would need to leave it there for 2 nights, which is not convenient for me at all.
Appears to start OK just that air or vacuum release noise happens
Any ideas would be appreciated

Thanks

[igorbmwx6]

Most likely these are your rear air shocks making the noise. If the car sits for a while, it can loose some of the air and then it will re-adjust itself by adding or releasing access air to/from the rear air shocks. I would be get alarmed over it.