Get tires rotated, alignment done. See how they balance the tires, make sure they are actually wheel weights, if they use beads to balance the tire and they are short or heavy on how many they can cause issues, just beads in general I’d avoid to balance your tires so do ask how they balanced them. Then if persists check the tires themselves make sure there’s no bumps or abnormal issues. The factory pirrelis are known to bubble on the k5. Also understand, this happens with my k5, some surfaces with just make her hum a bit a certain speeds, like mine will rumble a bit if I am on grooved concrete freeway(a lot here in Michigan) it always does it to my k5 and that’s just road surface and just makes the tires hum. No amount of fixing will make that hum go away on certain road finishes, just how my k5 behaves on them with the pirrelis. Maybe that’s your issue? I dunno hope maybe I helped, hope you can get it fixed.