Hey Hopeful! The MKC, since it's original release, has been lauded as being very quiet in most every way. Recently my wife and I returned from a 7,700 mile trip throughout the western/northwestern U.S. and we repeatedly discussed how pleased we are with many aspects of our 3 year old MKC, especially about how quiet it is at virtually every speed. Certain types of pavement will cause even the quietest of vehicles to "sing" or clatter but for the most part, we are pleased. Your use of the word "excessive" is something I've never heard used when describing the sound levels experienced in the MKC. I'd let the dealer have a look at it!
Mine is quieter than my X5 and every bit if not more quiet than my Range Rover Sport HSE. High praise indeed. Have dealer check to see if gaskets in doors are properly seated and also under hood. This vehicle for only 179 inches long, rides etc more like a true mid sized SUV in the 190+/- inch zone. Handles far better than the biased testing suggests as well. If they would dial in about 10% more firmness to steering in sport mode, they'd have the Germans VERY worried.
I have a 2017 Black Label with the 20-inch wheels and it is so quiet I am amazed. No wind noise at 85 mph, no noise from other vehicles passing by it is like a library. Have it checked as this is not typical.
Mine had excessive wind noise from the pano roof when new. Our dealer re-adjusted, and made it perfectly quiet. It took them 3 days to fix, but I drove a new MKX during this time. All was good. Make an appt, and take it in.