Heat pump hums depending on outside temperature

Hi everyone! Please help to understand the behavior of our heat pump. New building, 6 apartments in one house, built in 2022. Heat pump for hot water and heating. The technical room where the heat pump is installed is below our apartment. In the technical room are two large compressors and one smaller compressor, see pictures. Outside are two heat exchangers with fans. Depending on the outside temperature, we hear loud humming in the apartment. Sleeping is impossible. From about +5°C and upwards - there is no humming. From +5 to -5°C it gets stronger and stronger. From -5°C downwards it is roughly the same loudness. The compressors only have on/off control (according to the manufacturer), but it hums with different intensities, even when all compressors are running - I have checked that. And it always hums at the same frequency - 146Hz, see pictures. Recently, an acoustic measurement was carried out. Beforehand, I agreed with the company that built this heat pump that we would try the full load simulation so that we could be sure when it is measured. The colleague came, it was +3°C outside. He manually adjusted the target water temperature, turned the outside fans down, and manually activated the heat pumps. Then it really hummed. The colleague said that with slower fans outside, -7 to -10°C is simulated, and this increases the pressure difference at the compressor - it can hum more strongly. On the day of the acoustic measurement, it was +10°C outside. Everything was done the same way, fans were even turned down more, all compressors running, but there was hardly any humming. The acoustic measurement, which cost several thousand euros, was for nothing... Does anyone have an idea why the humming is so temperature dependent in this case? What is actually humming there, or what can be transmitted so well upwards, especially such a strange frequency of 146Hz? And what could be done if we want to have it measured again? Many thanks! Andriy

Did you also open the valves of the underfloor heating/radiators in the apartments during the measurement? What about the pumps?

Did you also open the valves of the underfloor heating/radiators in the apartments during the measurement? What about the pumps?

Thank you for the first response! No, we did not look at the valves. Which pumps do you mean? What idea do you have? We have checked it before as well, it does not hum when compressors below are not running, it hums lightly when only one large compressor is running, it hums loudly when both are running. The small compressor has hardly any effect. I have also attached a picture of what it looks like in the apartment.

Thank you for the first response! No, we have not looked at valves. Which pumps do you mean?

The heating circuit(s) have pumps that may be modulated, i.e., controlled depending on demand.

The heating circuit(s) have pumps that may be modulated, meaning they are controlled according to demand.

Could you please explain a bit regarding valves and pumps? Can these pumps run synchronously with compressors, or are they usually independent? Can you see the pumps in the photos? I have attached a few new photos.