so now i figured there is this hissing sound comming from the gas tank. When i had a problem with my power locks there was a hissing sound, so it looks like there is a leak in the fuel system. There are 3 lines comming from the tank, i know one is return, other one brings gas, and the 3rd one not sure, is it the line that pressurizes the tank, so guys help me here figure this, in my opinion there is a leak, so rite now the car only gets up to 3000k rpm's and than dies. Its 1995 Audi A6 with 116K, FWD. When i shut the car off, for about 30 seconds you hear this hissing sound under the hood.

PLEASE HELP ME!!!