High pitched squeek upon light acceleration on 2006 BMW 330i

I have a high pitched squeeking noise upon light acceleration. It seems to be inconsistant. But, you can hear it. Any ideas on what it could be?

Asked by for the 2006 BMW 330i
Sometimes you can hear a similar sound when the breather system (PCV) failed.
A BMW specialty shop should be able to check the PCV pressure with a manometer.

2 more answers
parking brake. just had mine fixed
If the sound is originating from the right rear wheel, it may be the brake pad wear sensor. It apparently will "flex" enough and make contact, producing the squeak. Really annoying; a local BMW shop should be able to adjust it, but it may set you back ~ $100. Design-flaw.