Quote Originally Posted by t_marat
Is there an auxiliary fuel pump?
Not up front. I remember reading about some BMW models having two fuel pumps but those were in the rear. One for fuel pickup and filtering, the second for pressurising the fuel lines to the engine.

I'm thinking it could well be the aux water pump even if I had the symptom when blipping from idle. Does it sound like the sound travels from the front-left to the dash and sides?