-fuel pump has 7k on it
-no start up issues (cranks on the first turn)
-problem only happens after driving for a while, starting the car and then turning it off doesn't cause the problem to happen

Problem:
I heard a faint humming noise coming from the back of my car the other day, even though the car had been turned off (for about 10 minutes). I realized that it could be my fuel pump that was still running, so I removed my gas cap to get a better listen. Once I removed the cap and released the pressure, I heard a slight knock and the noise stopped (I assume the fuel pump turned off). Could this be a fuel relay issue? Not sure why the fuel pump would still be running and then turn off when I opened the gas cap...Any suggestions?