air bubbles in fuel filter

[Daves55Sedan]

My 55 has an inline fuel filter with clear glass so you can see the gas inside. After the engine is shut off, there are air bubbles entering the filter from the inlet side (fuel pump side).
I gripped the inlet fuel line and it is not even hot, so the gas is not boiling. Is this a problem???

 

[frank long island]

maybe sucking air

 

[ford3]

probably one of the valves in the fuel pump leaking, most likly the suction side of the pump, if gas drains back out of the pump air bubbles will be seen replacing the gas, and a very good chance of a leak in the fuel system between fuel tank and fuel pump, check under car for a damp spot on fuel ine