However, thank you for all the good sugdestions and I will bear them in mind for the future. Especially re delay.

New Pianoteq user, immediately upgraded to Standard. I got three instruments. For my piece there is a strange background pulsing sound in any instrument. There was a very old post here suggesting to turn down the sympathetic resonance but that has no effect. It really ruins the playback. I do not know how to troubleshoot this. I am using Pianoteq in Dorico 6.

Just in case... try Pianoteq standalone and verify whether the same problem occurs there.

If it only occurs in Dorico, the first thing I would do is make sure you aren’t applying Dorico’s reverb to Pianoteq.

New Pianoteq user, immediately upgraded to Standard. I got three instruments. For my piece there is a strange background pulsing sound in any instrument. There was a very old post here suggesting to turn down the sympathetic resonance but that has no effect. It really ruins the playback. I do not know how to troubleshoot this. I am using Pianoteq in Dorico 6.

Turn off delay