I have a 2017 XE R-Sport RWD and since the very first winter I have noticed a clunking noise at slow speeds when turning in cold weather (below 50 degrees). I have had the dealership look at this multiple times. The first few times they said they couldn't find anything wrong and chalked it up to the car not liking cold weather. The last time they were able to replicate the noise and feeling in the steering wheel and said the rack n pinion needed to be replaced (the car wasn't even 2 yrs old). As soon as I drove away after picking it up the started again. I have 20" wheels and still running the factory installed Pirelli P Zeros.

Has anyone else had this problem? If so, what was the cause and fix? I know some about cars but this is something I have not experienced before.

 

Well, pretty sure its not cold weather-related
We get temps down to -20C occasionally without problems I think all cars get extreme cold weather testing.

Did the dealer fit a new rack? Your post isn't quite clear about this

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I think I can confirm it is the tires. I have a six week old 2018 XE S. I noticed it on most cold slow startup turns. I have 20” summer tires standard. We got our first snow and when I would turn the steering in snow at 0-5 mph speeds, the shutter and noise was alarming. I almost took it to be checked out at dealer. I have a set of snow wheels with blizzaks. Since I installed the winter wheels, zero issue. Kind of scary that a dealer would have changed out a rack not knowing the properties of high speed summer tires on cold pavement. Betting your issue is exactly what I described. All season tires will remedy your problem I would bet.