My 03 325i has the same symptoms as described by everyone above. I had my pressure sender replaced and oil/filter changed twice already. It only happens after the engine is warmed up and running for about 20 minutes when the engine is at idle speed. I tried Mobil One 10-30 oil which helped a little. I was told by a BMW mechanic that he's seen this on later BMW 3 series and to try Mobil One 20-50 oil and it can with stand the heat and increase compression.