Could still be your tires, I had this with a tire before, the thread on the outside was uneven which caused a vibration. Only fix was to replace the tires. Mine were one direction tires, so if yours are too, flip them around so they turn the other way. and when I say flip them, I mean put your right side tires on your left side and left tires on the right side. That way they'll be turning in the opposite. If that quiets down the vibration, you know its tires.