Go for a drive with anything lower than 1/3rd of a tank of petrol (even when runninng on gas) and come to a halt. Switch off ignition and hop out and what I believe is the fuel pump can be heard to be purring away in the tank. Seems to do this for several minutes then stops.
Only possible linked thing I've found is that when I unscrew the fuel cap the tank vents and it seems under the two or three times I've tried this the pump stops.
Doesn't seem to have same symptoms when the tank is above 1/3rd full (petrol)
Any ideas?
Lee D