If you have physical outputs routed to inputs, Bypass the UC mixer may cause a beep to be heard. Quit UC entirely and the noise will stop.
Secondly, UC uses multiple mixes. Main, 1/2, 3/4, etc. UC works independently of your DAW. Your DAW mixes and routes in its own way at the same time.
You either Bypass UC to mix only in your DAW,
OR
You manage your mixes in UC "and" in your DAW.