In order to cut the possibility of faulty tyres you could change the tyres temporary by borrowing from any one (friend or relative) or your other car (if u have). (I personally dont think its because of tyres)
If the sound persists then its definitely from one or more of your car wheel bearing.
Once i have had a problem in my previous reborn that exactly and literally exactly on reaching 80 Km/hr humming sound started inside the car cabin and the culprit was one rear wheel bearing. I replaced it and the problem gone.