2001 BMW 525i • 107,000 miles

Car has been making a whistling noise (possibly a vacuum leak?) That appears sporadically. It was first noticed at start-up, would increase/decrease in pitch with acceleration and then disappear upon warming up. More recently it doesn't appear at start-up consistently, but occasionally will start "down the road" and can be a little louder than usual then disappear. It would be hard to diagnose at a repair shop if it's not happening at the time. What do you suggest?
November 15, 2012.

The cyclone separator and its attached plumbing need to be inspected, is the noise louder when you open the oil filler with the engine running? If so replace the separator.

Dr. Hagerty
Nov 16, 2012.
The noise is intermittent, and now only happens every 2-3 days. I had a mechanic check the codes, even though it so far hasn't tripped the engine light. He couldn't find anything except for something to do with a lean/rich switch (?). I will see if the noise gets louder when the oil filler is open but I'll have to catch it when its actually whining/whistling.

Thanks for responding!

Nov 19, 2012.
Thank you.

Dr. Hagerty
Dec 6, 2012.