I've got similar issues. My setup also consists of MeanWell power supplies and Shelly RGBW2s (although mine run at 12V). As far as I can tell by the hours I've spent googling this issue, you can't really "fix" it. The buzzing/whistling sound coming from the PSU is generated by the PWM-Frequency used to dim the lights which in turn makes some parts in the power supply vibrate. The only solution I can see is to either try different power supplies or put them in a sound isolated box (may cause overheating issues). Another way of maybe solving this would be Shelly allowing to set the PWM-Frequency and test which values work out to generate the least amount of noise.
Also, I don't know if it's just me, but I was pretty sure that this issue wasn't as pronounced before the 1.9.0 Update. Maybe they changed the PWM-Frequency?
Disclaimer:
I am not an electrician and the information provided above is what I was able to gather from searching online and asking friends who are more familiar with the matter.