Aside from the normal startup sound, every once in awhile I hear a noise
that sounds like cavitation noises? Like what I'd expect if there is air
being introduced.. But I'm not smelling fuel, and there does not seem to be
any visible fuel leaks.

Almost sounds like a broken piezo buzzer?

First question is, how long has it got..

Second question is, my van never had a "front" fuel filter.. (Not since
I've owned it).. Maybe I should get one?

--t