Have same issue with 2014 Antara 2.2. Steering creaks especially in hot dry weather, took it to a guy who worked for Vauxhall but now on his own, he tells me its a design issue. Hot air from engine has to pass over steering rack which thats up and the knuckle joint drys out. Might answer why it isn't so bad when roads are wet!!.He put the car on the ramp for me to see, sure enough rack was too hot to touch, hopefully only needs the 2 knuckle joints on each side of the rack replacing.
Good old Vauxhall, more sh*** to deal with.