My fuel problems

Hi all, i have had probs with my fuel system for a couple of months now.   First i had a loudish humming noise coming from the back of car, although causing me no problems at this time, i had fuel pump,which is in petrol tank,replaced and fuel filter. The humming wasn't as loud after this, but have been told should make a bit of noise,is this right?
  Next i had humming noise from the area of the pump which is under the car,that sits next to the petrol tank. After being ok for a few weeks, last week every now and then, there would be a loud buzzing noise coming from the area of this external pump. While i was in a traffic jam, this buzzing got louder and eventually,the car cut out. It wouldn't re start straight away, but did after resting a few minutes.
  Over the next few days, the car would run fine if i was doing a decent speed, but as soon as i got in slow traffic, it would happen again.
then this week, the buzzing was there when first starting the car. My car,which is 92 GTI, is now in garage, having had this external fuel pump replaced, except that its not fixed the problem. In fact is running worse,coughing and spluttering and wont go over 3000 revs.
ANY IDEAS?? Checked older posts but although similar probs none exactly like this. Thank you for your time.

Luvbugz

Check out your fuel filters and check for blockages in the pipes BEFORE the pump.
Slightly different on a cab, but my Tin Top pump has a removable thimble shaped filter gauze on the inlet side which was catching crud from the tank, but restricting supply to the pump…

Thanx Al. car is in mechanics hands, he said today he thought it was a problem from the tank to that external pump.I'll mention the pipes to him. Been reading on past posts about cleaning or replacing the tank, do you think that would be applicable on a more recent golf like mine,i.e. 1992?
  Also, does anyone know who,in the Northamptonshire area, has the capability to do a pressure test, as my mechanic hasn't the equipment.
Thanx

Luvbugz