BMW Repair: 1999 328i engine sound at idle, crank case vent, oil filler cap

Question
My car has 38k miles on it and while at an idle it makes a continuous 'swooshing' sound. The idle is solid and it sounds like an 'air diverter?' in the intake system. No other symptoms are seen and the car runs great, just makes this weird noise while at an idle, either hot or cold. I can email a .mpg movie that details the sound.  

Answer
Jon, buy a cheap mechanics stethoscope at Sears or Harbour Freight and see if you can narrow down what area of the motor the noise is comming from. Noises are almost impossible to diagnose over the internet. Please send the file recording to slaughterfam@comcast.net. Check the rubber intake hose that branches off the main intake boot after the mass airflow sensor. That smaller hose habitually develops cracks on the backside radius and lets in unmetered air also creatiing an odd noise. Test for the noise with the a/c on and off. You can narrow components if this makes a difference. Check the Crank case vent valve (PCV). with the engine idleing turn the oil filler cap and just barely crack it open. There should be a little vacuum hold the cap down. Experiment with the a/c on and off. If there is a great deal of vacuum and the engine emmits a strange honking noise then the valve must be replace. Check those things and report back.
-Evan