Whistling noise from roofliner

Hey guys, I've only recently bought a CR-Z from a colleague of mine and I'm really happy with the car.
I however noticed that whenever I go around 120km/h (75mp/h) that there's a weird, whistling noise coming from the roof.

I've checked the antenna, that was my first suspicion, taped it off but the noise still came.
I've checked the windshield too, thats also not the issue.

Whenever I push or pull the roofliner however, it stops. Once I let go, it starts again.

Do you guys have any experience with a similar issue ? How did you fix it ?

Thanks in Advance <3