Vaccum Sound When I Turn On The X

[Blade69]

Every now and then, when I start up my X, I hear a little motor or vacuum sound coming from the rear compartment. Since I have the air suspension, I assumed it was coming from there. But why all of sudden is it doing it? It's only occasional. I can't pinpoint when it does or doesn't do it. Outside temp has no affect. I thought that since it was getting cooler and air is thinner that it was replacing air in the chambers. My vehicle doesn't raise or lower when I'm sitting there listening and looking while it's running. It's just weird.

I had some minor suspension work done (not to the air suspension though) and I can't recall hearing it before I had that work done.

Any help would be greatly appreciated.

[Bimmer Tool Rental]

It could be your DMTL pump. IT pressurizes the fuel system to check for leaks. It is located near the fuel filler assembly on most BMW's.

[Blade69]

It doesn't do it all the time. Just intermittently. Does that sound about right?

[killcrap]

The DMTL system only operates under normal conditions when the vehicle is off. All V8 equipped vehicle have air suspension. Depending if the vehicle has been sitting for a while, or has a leak in the air springs, the control module will turn on the air compressor to correct the ride height. The compressor will normally only run with the engine running, and usually noticed during cold start where the vehicle was parked overnight.

[Blade69]

Ok...so then I do have a small leak somewhere? :-(

[killcrap]

possibly, but you do not state if your vehicle has 0 miles or 150,000 miles. So hard to say whats wrong if you dont provide us with details.

[Blade69]

92K mikes.

[killcrap]

Measure the ride height when parked overnight, and then remeasure in the morning prior to starting the vehicle. If the compressor comes on, sometimes its normal, if it always comes on, then you have a leak worth investigating. Mind you, that most leaks on rear air suspensions occur past 150,000 miles.

[Helmuth]

Hm, now while I am reading that...... I seem to have the same from time to time. Bt I do not have air suspension. It doesn't sound like a compressor - I do not have one - more like the rear heat blower would come on for less then half a minute.