Trying to determine if there's a fuel starvation prob on ye olde vanagon, I
stop the car, leave it idling, take off the gas cap and listen for a sucking
sound, as in "this administration s...." (OK, wrong list.)  I don't hear
much, if any, noise from the gas cap removal.

Question: if there is a vacuum problem keeping the fuel from pumping
correctly, how much of a sound would I hear? Big noise? Or is it rather
subtle, something that could be imperceptible with cars going by, etc.?