I just had this problem on my '08 e90. It was the regulator/filter housing that's located under the backseat on the drivers side. If you want to inspect, just pull the bench out (just snaps in) and remove the round covers and look for gas. The plastic housing cracks over time. It's an easy job. Took me under an hour to replace the item in the link below. I recommend renting the fuel pump replacement tool kit from Auto Zone to remove the rings on the tank. It made quick work of getting the rings off and reinstalled.
https://www.bavauto.com/228-242-005002z