That is a good description of the noise and issue. My 2020 Denali 2500 6.6L makes the same noise. I assume other posts have a Duramax , so it’s not an engine issue. I found a technical bulletin regarding power steering noise on earlier models but it is related to extreme cold weather (-31 deg F), so maybe it is fluid related. I wish the dealer would just try the fix to see if it works in warmer conditions. The noise is very annoying.
I will attach the tech bulletin. Please update what your dealer says.
mc-10163270-9999.pdf