Some of you my have heard this noise on your engine,,,,sometime on BMW your venting system on your valve cover might go bad,,,,and when it does you may hear a hooting/chirping noise at idle,,,,,and when you release the oil cap the noise goes away,,,,that tells us is that the valve cover has gone bad,,,,so we replace the valve cover and the noise should go away,,,,but not all the time,,,,some time the valve cover does damage to the rear engine seal by sucking it in,,,,and sucking air past the seal causing that hooting/chirping noise. Here the old seal removed,,,sometime when the old seal gets sucked in it very hard to remove,,,,I found out just drill a couple small holes in it ,,,,and screw     a small screw into it,,,,then take some pliers and grab the screw,,,,now you have some to pull on and take the rear engine seal out.