I have a 96 Chevy blazer we went to six flags yesterday and on the way home when i let off the gas it made a weird noise it was like a humming sound like when you are on the interstate and when you get off to the side and hit the edge where they have the groves cut in to wake you up if you doze off.When i let off the gas and the more i slowed down the louder it got. Put it in 4 wheel high and the noise stopped any ideas?