Hi guys. I drive a Polo GTI 1.8. Love it or I used to before I started hearing a hissing sound when I accelerate with the windows down or sunroof open. The hiss/swoosh is similar to when a car is fitted with aftermarket HKS and Forge dumbvalves or blow off valves. It is much more noticeable between 0 - 100 and more so when the car is underload. Revving the car stationary with the bonnet lifted, the sound can be heard from the passanger side, at the rear end of the engine.

Iv also noticed that the car is a bit lathergic and the power/boost is erratic. When I bought the car it did not have this sound.

I have taken it to the dealer that sold it and a reputable vw workshop. Boostleak tests have been done and no leaks found. The PCV and the Diverter Valve were replaced and this did not rid the car of the noise.

Some hold the view that the sound is normal.But Im not persueded as other cars like mine do not make the sound and as I have indicated, I did not have the sound before.

Can I have your 2cents guys.

Sounds like your actuator maybe stuck or failing. You are going to loose a turbo if you don't sort it out ASAP