Fuel pump woes

[subeylube]

Hi, im back so be nice.
I have a my05 2litre imprezza that been in the family since new, currently 35000klms

Some time ago the fuel pump started to howl, so I fitted a new one, all good. noise gone.

Couple of weeks later noise back, but not as bad, but audible at 60 klmh with radio on. No duff duff just radio at normal volume.

So new fuel filter, check fuel pressure and flow, check fuel pressure regulator, all good, and the old fuel filter was unrestricted.

After listening to the new pump for a while ive noticed it definately noisier when the tank is full?? In fact with the tank half or less theres hardly any noise, and none audible in the car. The replacement pump was a "Denso" brand if that helps.

Any thoughts