What type of speakers are those?
The noise level changes when you change the volume on the front panel?
Do you have that noise only on the Main out or do you have a same noise on the Headphones out and or DB25?
I use Mackie CR4 but I also check the main output using two channel s on my mixer and it has been the same high pitch noise, I checked the headphones output and it working good, unfortunately, I and not able to check the 25D-sub connectors right now.
This sounds like some grounding issue.
I mean internally the headphones and main out 1-2 uses the same internal audiobus.
If you don’t hear that noise in the headphones out that’s sounds like some issue between the uTrack24 and the receiver.
Your cable connection is balanced or unbalanced?
Do you have a chance with a wire connect the uTrack24 chassis to your receiver chassis –> does it make any difference in the noise?
You take a solid ground point on the uTrack24 (like Wordclock connector ground) you take a similar ground point on your receiver (like XLR ground on your mixing console) and you make a connection between those two point using a raw wire.
Does your receiver and the uTrack24 connected to the same power outlet?