rear axle whines at 79mph and at 84 mph

I purchased my fourth Silverado new in 2014 from hendrick in hoover I have had to have this problem repaired twice with no relief and was told that they have done all that they can do? and my issue was with Chevrolet I contacted them and was given a case number and several days later I was contacted and told that at 79 mph my truck would not be covered or repaired at that speed as it exceeds the speed limit as if it is not designed to be driven past 70?? and I would not be offered and extra trade assistance from general motors at all to try to trade into another truck this is how Chevrolet treats its customers and this is not the first time I have contacted Chevrolet about a problem and I was given the same results no help at all as if they don't care after you purchase there product and by there actions don't want you to purchase another product from them at all as this is my last chevrolet that I will ever purchase because they don't stand behind there products and don't care if you purchase another one from them! because all of the pickups still have wind noise and when you purchase one you will just have to deal with it as it is a defect that all Chevrolet pickups have! drive a ford they don't have any wind noise! my next truck will be a ford! thanks Chevrolet!