No Boost s3

[Baptistebellevaut]

Hey Guys, this is my first time using a forum to get some help. I bought my s3 8p back in february and it worked perfectly fine until about 2 months back. I was just driving as usual and did a Pull from about 50kph to 10kph and immediatly started loosing power. since then i replaced the n75 and the Blowoff and even gave the car to a mechanic so they could check if there was any leak. They couldnt find anything. they also couldnt find any error codes except for some misfires. Now the mech told me its probably the turbo but today i drove the car again just to see if i could find anything. When i rolled down the windows and accelerated i was able to hear a clear noise that sounds like pressure getiing out of somewhere. Like a "PFFFFT" so it made me think is there a chance there actually is a leak or where else is that sound coming?
Sorry for my bad english im trying my best.
Thank you guys in advance