Hello Listees,

I need some help correcting a noisy fuel pump. The noise is 
"zirrrrrrrrrt……..zirrt…………..zirrrrrrrrrrrrrrrrrt" and is audible only at 
idle.  It used to occur only when the tank was almost empty, and immediately 
disappeared after topping up.  I recently replaced my gas tank (it was 
collapsing due to venting problems, which I think I've solved), and ever 
since then this noise is a constant companion.  One thing different since the 
tank swap: my new tank requires the use of a small square plastic filter 
between the tank and the pump.  This pre-filter is translucent, and upon 
inspection while the van is idling, I noticed there is not a constant stream 
of fuel flowing through it-there seems to be air bubbles being drawn through 
the filter and into the pump, which I think are causing the noise.  What is 
going on here?  I've replaced the line between the tank and the pre-filter to 
correct a leaking hose (and thus air being sucked into the line) but to no 
avail.  All connections are tight.  Is this a sign of a bad fuel pump that 
(coincidentally) got worse with the tank change/pre-filter addition?  Bad 
fuel pressure regulator?  Clogged pre-filter?  Or perhaps there is too much 
flow restriction with the smaller fuel outlet pipe on the new tank (old tank 
was 12 mm, new is 7 mm or so) and the addition of the pre-filter, thus 
creating a vacuum in the line?

TIA,

Philip