My Blazer has an intermittant problem with, I believe, the 4- wheel drive. Whenever I put a load on the transmission, such as driving up a steep hill or mountain, or driving over 70 mph over even just several miles distance on the fwy, it will make an awful grinding noise coming from the passenger side, where the wheel bearing would be. Especially upon slowing down, such as to exit the freeway. Once I stop, and then go again, the noise is gone. Or, in case of a hill, if I start going downhill. The first time it happened, it was towed to my mechanic, and he replaced the right wheel bearing, which was bad, and the driver's side as well. It was fine for about a month, until I drove about 70 miles on the freeway, going 70 to 75 mph. Upon exiting the freeway, the grinding noise started again. Please help!

 

could be the drive shaft if a u joint is getting ready to go or if it isn't balanced should check if yours have grease fittings they are tucked in the slots just found mine after getting a grinding noise greased them now it is fine