Window seal / Door seal makes strange noise

The REGEL-Air window rebate ventilators nowadays have small return springs that prevent the flapping of the flaps.

Is something like that missing in your system? Or is it perhaps missing only in one of the ventilators?

By the way, the missing seal at one point of the window is normal for window rebate ventilators.

Is it missing in your system

Thank you for your suggestions.

The window rebate ventilators are installed in almost all windows. Only the lift/slide element, to my knowledge, does not have one. They all look the same. They all also have the two "movable" parts. And I see no return or damping springs anywhere.

Your window rebate ventilators are ari... your type is the latest design, there are no springs and no freely swinging hard plastic flaps.... Look up the website and read up on it.

I also have Brömse in the house, type Premium 2.0. Why did you have the window rebate ventilators installed? Don't you also have a ventilation system with heat recovery?

Why did you have the window rebate ventilators installed?

It was standardly planned that way by the house construction company. And the manufacturer also installed them that way, or rather, they were already in the window/door sashes.