BMW Repair: 2002 BMW 530I, oil dipstick, 2002 bmw 530i

Question
Last seven digits of VIN - CH90018
I have a 2002 BMW 530i automatic purchased new in 2002.  I only have 15,330 miles on it.  I drive this car mostly during the week ends.  After driving it for a while maybe from 5 miles on or when the engine is fully warm up I hear a sucking sound at the intake manifold area after I turn off the engine.  If I start the car again and turn it off, the same thing happends.  I have this problem since I have 12000 miles on it.  Today, the dealer here in Honolulu replaced the oil vapor separator (similar to PVC or PCV valve). This did not solve the problem. Dealer says no fault codes was detected.  If you remove the engine oil cap or the oil dipstick while the engine is in idle and turn off the engine the sucking sound goes away. The car runs perfectly even I have that sucking sound after I turn off the engine.  I have this checked by one of their techs in Dec 2005 when I have 12000 miles on it. He did mention that the sucking sound is the air coming out from the intake manifold.  Nothing was done at that time. Is this normal?  Even the shop foreman is puzzled. Please help.  Thanks !

Answer
Anselmo, check for intake manifold leaks (gaskets, intake boot at idle valve connection, Vacuum brake booster, etc.) Make sure they are using a smoke machine to detect leaks. I have seen the Disa valve on the side of the intake manifold make odd noises when it fails. Talk to Technician Casey S. at Honolulu BMW and take him out to lunch and ask his opinion if he still works there. I used to work with him at a dealer in California and he is a good knowledgeable guy to speak with. Noises are hard to diagnose especially when I can't hear them. Good luck.
-Evan Slater