Raspberry Pi noise issue

Hi all,

After some lurking here (thank you all who have posted advice on the subject) and much tinkering I now have a functioning Pi 5 device running Pianoteq 8 Pro with a 52Pi NVDAC hat. I have mostly followed Jimmi's installation instructions, though with the standard Pi OS rather than the light one, as my linux skills are not quite up to the task of doing this all via command line.

The one final issue I'm hoping to resolve is a faint buzzing I hear when a key is depressed (even if the key is depressed at a low enough velocity that no instrument sound is produced). The frequency of the buzzing appears to be the sample rate divided by the buffer size, e.g. at 48 kHz and 128 samples the noise frequency is 375 Hz. I'm using decent quality Hosa cables and everything is very quiet when I'm not playing.

Does anyone have an idea what's going on and how I can eliminate or mitigate it?