Weird sound

I have a 2006 pontiac g6 with 57,000 miles. The car is in great condition. At about 45,000 miles the car started to make a weird humming sound coming from the front of the car. It does not make the sound when you are stopped. It only starts when you get up to lets say about 15 to 20 mph and up. I have just put on new tires and replaced all 4 disc brakes. It has made no difference in the sound. When it first started out it was very subtle and progressed to a louder sound. I have checked to see if something was draging or if the tire was rubbing against something but everything looks sound under and around the car. What could it possibly be? Thanks for any suggestions.

Could it be wind noise? I once had a Rambler that had a humming noise that was in the grille. It would start at about 45 miles per hour. Also, I once had a rental car that had a terrible buzzing noise in the windshield. I took it back and was given another car. Apparently, the windshield had been replaced and not properly sealed.

Have the wheel bearings checked

I would guess wheel bearings. Although, 57k miles is pretty low for failing wheel bearings, but it is the likely culprit.

I had a wheel bearing go out at 20K on a new car and others last several hundred K so you never know. When you get it up to speed, put it in neutral and coast on a smooth road to see if it still does it. If it does, then something in the wheels or drive train. If not, then engine related like pulley, etc. You can also turn the steering wheel a little side to side to see if the noise changes. That would indicate a wheel bearing.