Having trouble figuring out why the fuel pump is apparently creating so much
vaccum in the tank that every so often  I hear a loud clunk coming from
under the van.  This happens while driving, shortly after I shut the motor
off at a destination, and definitely when I remove the cap when refillingthe
tank.  I lazily replaced only one of the check valve asemblies(pas. side) up
under the front fender wells, so can thedriver's side totally clog up and
cause this, or is there another source of the problem that I'm not thinking
of.  Tank fills up just fine, not belching of gas, and the crossover pipe
and grommets are maybe 6 mo. old.

I'm going to assume that the fuel pump isn't being harmed by this vaccum,
but I'd rather have a clue as to whereto go from here.

DM&FS