Summary: warm engine re-start attempts results in violent sucking sound from fuel tank area

After driving the the XJ8(1999 with 45,000 miles) for 10 to 15 miles, then parking it and tuning off the engine for 30 minutes or more, an attempted restart results in a violent sucking sounds and rattling sounds (similar to the sound a straw make when you are trying to get the last of a soda out of a cup). It will then not start or idle like a cold engine, but instead it requires pumping of the accelerator pedal to get it going again and only after several attempts.

When starting the car a few days later, it started cold and without the noises. Considerable gas fumes are occasionally present. I am guessing the noise is the fuel pump trying to pump fuel up to the engine but having trouble doing it. Or, could this be a vapor or injector issue? I just don’t know. Any help will be much appreciated.