I know that the code PO440 means a evap. system leak but I'm a little puzzled. I jacked up the car and the noise that I notice is coming from inside the gas tank. I'm not sure whats wrong. Can anyone help?

 

I had the same code thrown and all it turned out to be was needing a new gas cap. It could be another small leak in your evap canister or in one of your hoses. Try the joints first if the gas cap isn't the issue. You'll only notice a drop in gas mileage until you fix it.

 

EVAP codes can mean a few things. Here's the generic ODB-II info on that code:
OBD-II Trouble Code: P0440 Evaporative Emission Control System Malfunction
The noise you hear from the gas tank is probably the fuel pump (they hum when active).
Sometimes an evap code can be as simple as a loose gas cap or a leaky gas cap. A friend of mine has a 3800 powered '97 Grand Prix. He got an evap code and we found some dry rotted vacuum lines, replaced them, cleared the code and for a couple months now, no problems.