Real oem lists them on diesels in Europe but not on petrol so as already mentioned it's there to stop the engine noise by the looks of it, but it does list them on US spec 228i but not on the M235i
http://www.realoem.com/bmw/enUS/show...diagId=51_8650
http://www.realoem.com/bmw/enUS/show...diagId=51_8650