Heat pumps require a lot of energy and make noise

Only 80 sqm of living space is heated, at 21 degrees. The rest is set to 15 degrees.

In new buildings, always heat all rooms evenly.

P.S. It is a fallacy that you only heat 80sqm. With 80sqm of heating surface, you are actually heating the entire house. It’s like a refrigerator—you can’t say you don’t cool the middle shelf.
And with that, you have messed up the heating settings = the problem you described.

Are there any general answers to this?

That is definitely a problem.
Especially a heat pump relies on heating surface.
If you turn off half of the heating circuits, the whole house has to be heated with the remaining circuits.
That means the flow rate and supply temperature have to rise significantly there to compensate for the other rooms.

Because you always have to remember, normally houses are only insulated on the outside, but not between the rooms.

So it is okay, for example, if you want to turn down the bedroom by 2 or 3 degrees, but please not half of the house by a full 6 degrees.
So start with normal settings, see if the problem is solved, and then please report back.

We also had the whistling HKV, handed over by the GU like that. That comes from heavily throttled circuits. Here you have high flow velocities, which then cause the whistling.

So turn everything fully open (at the sight glasses AND under the ERR caps), possibly close any existing bypass valve, always keep all ERR fully open or dismantled.

Then do the balancing. It sounds more complicated than it is.