Controlled residential ventilation - You can hear every word in the other room - Is this normal?

The flexible pipes probably have soundproofing properties, but based on the installation position, their task is to dampen the noises of the system.

Between the rooms, telephone sound dampers would need to be installed. Then it fits.

Well, it depends again on what was ordered. If the order was:

One controlled residential ventilation system, please!

Then a controlled residential ventilation system was built.

In my contract, for example, it explicitly states that sound dampers are installed here and there and they are also marked on the plan.

With your variant (by the way, the spiral-seam ducts are the better option in terms of maintenance, etc.), retrofitting is quite simple.

You can still hear the system humming loudly through the supply air valves. Even when it's only running at 30%. It is quite disturbing when lying in bed.

What type of system is this actually?

The offer only includes controlled ventilation with heat recovery via a counterflow heat exchanger. It is from Nibe, unfortunately, I cannot find the exact designation. As heating, we have Nibe Fighter 2040-6 with indoor unit VVM 500. If that is important?

Then it is probably also a Nibe device. For example, ERS 20-250 as an addon or GV-HR 130-250 as a standalone device

How large is the ventilated living area? Both devices provide a maximum of 220m3/h, which is not a lot and causes the device to constantly run at full capacity ...

In the datasheet for the first-mentioned device, it says 47.5dB at a distance of one meter from the device with an air flow of 105m3. Uff. That is not little. How loud it is at full load, I have not discovered yet.