That's because when cold, rubber is less flexible, and grease in the strut bearing (ball bearings) is more viscous. Rubber also gets drier and potentially less flexible with time and wear, just like tires can dry rot and have cracks. If you have any cracks in your mounts, which brings more movement & play, then you are trying to flex cold old rubber even more on bumps and dips.
If you are not aware of the known wear parts of the strut mount and bearing, here is a video. Notice how he says noises you hear when going over bumps, that's when you can hear certain strut mount and bearing issues and it doesn't have to be completely broken like in the video. This noise is not unique to the XC60 as other Volvos and other vehicles makes can suffer from the same symptoms. There is a saying a car battery dies in July but you won't realize it until December. It's similar to rubber suspension parts because the cold affects the rubber's flexibility.
How many miles are on your XC60?
If you have over 60k-80k miles, then you might want to start planning for sometime in the future to replace the strut mounts and bearings (they should be replaced together).