FYI: The drain cowls are on each side of the engine compartment near the fire wall. They are plastic screens the can be easily cleaned out. I suspect its probably related to the AC evaporator drain tube. Maybe somebody can post a picture of the part.
2010 E93 335i M LeMans Blue
2001 E 46 330ci Coupe/silver/black/Sunroof
1999 BMW R1200C Cruiser-Ivory & Blue