The ventilation system is loud and disturbing

No, those are turntables that can be screwed further in or out.

Maybe a picture of it would be helpful? It certainly can't hurt. Because it is a central ventilation, I am interested in how high the ventilation flow is, and whether any calculations have been done for how much it should be per room? During the internal commissioning, they placed foam rolls in the duct to make sure it was correct. With us, we could hardly hear anything. Except if we were standing in the utility room next to the unit. But that was a combined air-water heat pump/ventilation system. The installer also said that it could be noisy if the ventilation filters are not cleaned, but if it only runs for 1 month, I can’t imagine that.

There was no commissioning, no technician, no expert, no calculation, no one who knows anything about it. Our landlord screwed the thing to the wall and pressed the start button. Yes, unfortunately ... :-(

Where is the device located? I have a central ventilation system and I hear exactly ZERO from it.

So:
- Is the ventilation device located in the basement/utility room with a soundproof door?
- Is there a silencer after the ventilation device?
- Are ventilation ducts in the screed?
- What do the inlet/outlet vents look like?
- What ventilation levels are there and which one is it operating on?

You can turn the plates in the slots though?! If you turn them, it should be quieter…

You can turn the plates in the outlets, right?! If you turn them off, it should be quieter…

Rather the opposite. If the same amount of air has to pass through a smaller opening, it gets louder. Maybe it will eventually start to whistle like with leaky front doors and windows.