Air-to-air heat pump experiences?

You don't seem to be very enthusiastic overall.

What I would also be interested in is your opinion on acoustic insulation? How "sound-permeable" is the house? Can you hear music upstairs without those downstairs noticing? How loud are passing cars roughly? I have read that in wooden houses high-frequency noises are still well filtered out, but low-frequency noises like bass or car engines are heard very clearly?

That depends on so many factors that it cannot be answered objectively here.

A timber frame construction can be acoustically insulated just as well as a solid house or just as poorly. And disturbances like traffic noise or music also depend on the circumstances. How far away is the street, how loud is the music, and which frequencies... and in the end, the "main problem" is still the person who hears/does not hear it.

Timber frame construction is certainly somewhat more sound-permeable, but as I said, there are extreme differences....

Why don't you inform yourself about a [SoleWärmepumpe] with [Erdwärmekörben]? You don't need deep drilling, it works practically everywhere, has a much better balance than an air-to-air heat pump or air-to-water heat pump, and is whisper-quiet.... The [Erdwärmekörbe] are buried below the frost line (about 1.5m) in the garden. No permit required.....

so it is generally very noisy. no comparison to the old apartment in the solid house.

why not very enthusiastic? I only wrote that it is very noisy but that does not bother me at all. the dry air in winter does, but one will get used to it.