hissing noise right before shifting 2/3 and 3/4 after driving on highway

Hi there from Austria,

I'm currently wondering what has gotten into the landy (2010 92000km), because after driving on the highway for a while, leaving the highway and accelerating right before shifting from 2. to 3. gear and same with 3. to 4., when releasing gas and pushing clutch i can clearly hear a hissing noise. After a while the noise discontinues (approx 30 minutes). When not driving on the highway, there is no such thing as a hissing or else.
Checked the hoses of the turbo, they seem ok.
Could it be a sign for a worn out v-belt, waste gate or turbo?
Service Point couldn't find anything on the checkup.

Thanks for your help.

Check the brake servo, and the hoses between it and the vacuum pump for leaks. The vac pump is located on top of the coolant pump.

Hi there,
just checked them. Found no leaks whatsoever but at the moment i didn´t drive at the highway, so i will check it tomorrow.
What i saw was that behind the intake manifold there was an oil film on a screw and also on a plug, but not that much, car isn´t leaking and the same is with my dads´ puma.
The starter was changed in july, but i don´t think that there is any connection with that, even if the mechanic was doing rough work during installing it.

I managed to get a video of the noise a few days ago. When watching the vid in the zip file, between 3 and 5 seconds you can hear the noise.

Thanks for your help.

So apparently 5 bolts out of 10 holding the intake manifold were a little loose so i tightened them. Tomorrow I'll have to drive on the highway so we will see.

I'm curious if tightening the intake manifold bolts fixed your hissing sound?