Hi

These suffer from injector seals leaking combustion gas into the fuel rail in the head. worth checking return from engine for signs of bubbles.

I think one of the above posts was thinking similar as it often results in noises from pump.

One of the ports on the filter housing has a small valve to bleed of small amounts of trapped air.

Also pretty sure there is a gauze filter in the head rail port, which can restrict flow if blocked

Cheers Aidan