That explains the air noise....cavitation.
It causes the air eliminator to expell the air through the vent.
Any leak in the pipe before the pump will cause air to get into the system while pumping (vacuum), and will leak fluid when the pump is not running. (gravity pressure)
This is only for pumps.... not dispensers

Veeder Root Rebuilds.....since 1987
Veeder Root Identification CD
Gas Pump Clock Repair
jkyocom@bellsouth.net