Many are fighting this issue with no real conclusion as to it's cause or how to fix it. Some have had their power steering bracket changed and fixed the problem, others a pulley or two, etc. Mine is doing it and is killing me slowly. I've changed my belt to a gator back and no dice. I don't care to spend a fortune trying to figure out Chevys issue. Too many trucks doing the same thing to be a coincidence. I asked my stealer about the issue and they say they never heard of such a problem. Service counter guys says his does it and he changed his pullies and still has the chirp but he says it's because he didn't change his belt when he changed the pullies, Whatever!!!
Anyway, Good luck on fixing it, I'll likely go after it someday but I have another car I drive so it barely moves so it's only a pain once in a while.
'15 2500HD CC standard bed (all stock)