Check your Cabin Air Filter. they are very easy to get access too. If you find a DIY for an Oil Catch Can, it covers the steps necessary to remove the shrouding covering the filter.
If you still have warranty on your car, BMW will switch it out for you. BMW recently replaced my filter during a routine service. I had no issues with the old one.
MY Build Log
08 AW 135i | Cobb | ETS FMIC | ER CP w/ Tial Bov | AR Catted Downpipes | Berk Mids | Meisterschaft GT SUS 1M |M3 Control Arms | M3 Sways | M3 Rear Subframe Bushings | Wavetrac LSD | AST 4200 DA Coilovers | HRE R43 | Hankook R-S3 |Full BMW Performance Interior | Revozport 1M Raze Aero Package in Satin Carbon |1M Body Conversion|