A clogged filter or tank screen can cause something like that.. What can happen is that as the filter or screen clogs, the pump keeps on pulling, and since it can't suck enough fuel through, it begins sucking whatever it can, through whatever orifice, meaning air bubbles. A connection that is normally secure might begin to leak air when subjected to serious suction.

I'd check the filters and tank strainer first, and if they are OK, then go on to the hoses and hose connections like people have mentioned.

peace,
sam

__________________
"That f***in' biodiesel is makin' me hungry."

1982 300TD Astral Silver w/ 250k (BIO BNZ)
2001 Aprilia SR50 Corsa Red w/ 5.5k (>100 MPG)