In turbo charged engines, sometimes you can observe a Hissing sound while engine is running.
Inorder to ensure that , the source of this noise, you can unplug the turbo vaccum hose and try the engine running. Now if you dont see the hissing noise, then there is a sure chance that Vaccum Leak due to Turbo Vaccum hose is the reason for the hissing noise.
Sometimes, you will see a warning signal in the dashboard if vaccum leak has occured.
Vaccum leak usually needs technician experts assistants. So it is advisable to take your car to a well known technician to solve the issue. But if you are more sure about that the leak is due to the damaged vaccum hose or hose connector, then you can replace the hose alone by yourself to save some money.