track down the hissing...pop the hood and rev it from the throttle body....you should be able to get a pretty good idea of where it is coming from...a tethascope will definitely help....

 

I talked to audi tech at school. I goto UTI arizona, they are fixing the boost leak Monday. As for the gas tank the instructor said its baffles in my fender well that are not opening for the gas to go into the tank. I just have to pay for parts and school will fix it for me.

 

Check for codes.