bad engine pressure
This problem came up the other day, and I really haven't been able to figure out what it is. First off, I have an automatic 318is. When the engine runs for a few minutes, a whistling noise comes from the engine bay. It's really difficult to pinpoint exactly where it's coming from.
I first thought it was the pulleys but I've noticed that when i lift off the oil filler cap, there is a noticeable pressure coming from inside the engine. The noise also goes away when the filler cap is taken off. It must be a valve that is sucking in more air than it's supposed to, but which one could it be?