Following on from my on going problem, as above what would make a pump get noisy?

lack of fuel?
sucking in air?

The pump is fine when car is warming up but then all of a sudden the pump becomes LOADS more noisy than usual and it causes a fuel pressure drop.

Basically i have been ticking things off the list of potential causes and so far i have replaced the pump and fuel pressure regulator with new items and rewired the fuel circuit.

Yesterday an auto electrician came and checked over the new fuel pump wiring circuit that my mate Rob did for me. Car is running a direct feed from the battery now to a new relay switched by the inertia switch.
When car is running the battery voltage is just under 14v and when lights and heaters etc are on the voltage is 13.38 or so. The pump is pulling 9A current. are these figures acceptable?

The fuse links to battery seem to have already been replaced with a proper fused wire.

The sparky also checked the battery to alternator wire. the alternator end was a bit crap so he cut the wire back to clean stuff and soldered on a decent new connection. this upped the charging voltage at the battery by 0.5V.

He reckons that the wiring is all fine and not likely to be causing the noisy pump. BTW when the pump gets noisy the current drawn doesnt increase so it isn't that.

So what could cause a noisy pump?

Only thing left to do is remove the tank and clean it out with fresh fuel then replace the filter.

any other suggestions?

chop