gas tank vacuum

What is your question?

no engine light codes.I am guessing A vacuum builds in the gas tank and when released within 5 min of turning off a "ping" sound is heard that resembles what I think is the gas tank resuming its original shape. I checked and found No connecting hoses plugged or pinched. This started after the tank was removed and new pump installed. What should I be looking for or how to test the carbon canister for fumes to flow freely? It happens in warm or cold temps.