Diesel fuel pump in the tank or in line?

[treeman]

I have a 2003 E53 3.0d diesel X5 and my local mechanic thinks the fuel pump at the tank end is not creating enough pressure to prime the high pressure pump by the fuel filter which makes the car not start.
Does anyone know it the pump is in the fuel tank or in-line outside of the tank?

Hoping for the latter as would consider changing that myself.

I hear the pump making a noise all the time the key is in position 2 (Run) before cranking the engine. Does anyone know or can check if theirs only makes a short pump noise then stops - only I wonder if the pump is constantly whirring as it's not creating enough pressure.