there could be a few different places that it could be coming from around there. try getting a spray bottle with some heavy soapy water and spray it around all your CAC tubes around the area you hear the sound. if you see bubbles you found the leak. there shouldn't be enough pressure in the delete to cause the hiss. could also be that your down pipe isn't seated all the way against your turbo. they can be a bear to get to seat properly sometimes. let us know what you find out!