How do i know which fuel pump?

[roccit_53 at scirocco.cs.uoguelph.ca (C Boyko)]

Okay, let's say this is my 16V (It's the Cabby, still). So I pop hatch #1
under the back seat, and I can hear the transfer pump, but it's more of the
same "wizzle" sound. I changed the main fuel filter, and there is no crud
either in the tank or in the screen to the transfer pump. So now what do I
do? I've buttoned it back up and will work on a few other projects till I
know what to do next, one or both of these fuel pumps is most likely toast,
the question is, which? 
Would the sound get transferred up to the tank? It's much louder in the car
with the seat out. (I'm hoping  the in tank pump's the bad one.....the
other will be a real bitch to change I'm sure)

Thanks for you reply eh?
cathy