TD4 Under Bonnet Fuel Pump Noise

Folks, Advice please.
2002 TD4 Under Bonnet Fuel Pump Noise.
Halfway home tonight I noticed a buzzing from the engine bay, later found this to be coming from the under bonnet fuel pump. Checked the in-tank pump and appears to be OK, I can hear that one running (almost silent).
Cannot get the part number of the under bonnet pump without getting tools out but I think it’s a WQB100480L (TD4 March 2002).
Is it safe to say the under bonnet pump is on it’s way out? Any advice for changing one of these?
Thanks,
Chris T

It could be that either the tank pump is caput or its input is blocked. This would require the under-bonnet pump to suck all the way from the tank causing it to cavitate and make a noise. Sucking in air somewhere along the pipe would also have the same effect so you could check all joints.
Cant remember whether the fuel filter is before or after the second pump. If before, a blocked filter would also cause the the same problem. Has it been changed recently?
Whichever it is, your engine is likely to stop soon as there is a pressure sensor on the pump outlet which stops the engine running if the pressure is low. This is to protect the HP pump, which is very expensive, from cavitating.

hope thes are of help

Thanks for the replies.
Ordered a Lift Pump yesterday and fitted it today. Problem sorted. Give the car a good run and no problems. Tank pump sounds to be running with no probs.
Chris T