Tried to leave this to my tuner to sort out but it he is none the wiser so maybe someone on here can help PLEASE

When I start the car early morning or when its been stood for a long time the fuel pump primes up and i can hear a knocking sound for about 5/7 seconds coming from what seems to be the metering unit or that area. The car will start straight away before the knocking stops but will run rough for about 30 seconds then clear and the car will drive OK. this happened before and after my recent engine rebuild due to the head gasket blowing.

New items that have been changed with engine rebuild or I have done in the last few months

Cam
springs
followers
turbo
all water and oil hoses
injectors serviced/flow tested etc
plugs have now been changed ngkbc8
distributer cap
rotor arm
leads standard ford and a few other bits and bobs but nothing else to do with fuel directly

When i take the plugs out and have a look after 200 miles of driving number 4 is white while the other look brown and fine

I have recently bought a nearly new metering head thats winging its way to me this week hoping that this will cure the problem.

Anybody had anything similar happen or have any ideas at all? this is with and without the cold start valve connected as well

CheeRS