Rear driver side brakes making awful creaking sound

[Conky105]

Yea, sounds like dry movement of caliper and/or hardware. Especially since you are not moving. Looks like a little rust in there. Live in a salt on roads state?

I had the same issue on my 2019 Yukon also. Turned out it was the caliper slide pins. They needed some sil glyde grease. Problem solved.

 

[Conky105]

I live in the same climate as you to. Snow and salt in the winter.