my truck recently feels as its pulling to the left. sometimes it does and others not. when i let off the gas its when it does it the most at higher speeds, also sounds like a humming noise.after 40mph its not so bad. had brakes and rotors checked and is fine. its an on again and off again thing. was told was maybe the 4 wheel drive was interfering. dont want to pay for a diagonist computer check, was wondering if i really needed it. any suggestions?