2006 GMC Sierra z71 speed related grinding

[Kelsey92504]

I have a 2006 GMC Sierra z71 has 159,000 miles on it. I've already changed the front hub bearings and the tires are brand new. Brakes are in good shape as well. I also had someone check the front differential bearings too. Said the front diff was good. The noise starts at about 50-55 and keeps getting louder with speed. The noise is similar to a hub bearing noise. When you let off the throttle the noise is more pronounced then when on the throttle. I'm thinking it's te cv axles. The cv boots don't have any tears in them and I have no clicking noise. But I've also heard that cv axles can make this noise. Also the noise seems to change when I hit bumps. that's also why I'm thinking cv axles. Because cv axles are the only thing that move with the suspension and also rotate. Let me know what you all think.

[rags1317]

I have the same truck and had the same noise. Always thought it was coming from the front. but turned out it was the carrier bearings in the rear differential. When I checked the fluid it was low and black. Took off the cover and only about a quart of fluid came out and everything was black with a lot of metal on the magnet. I rebuilt the diff and everything is quiet

[Kelsey92504]

This is interesting. My front diff fluid when I changed it was metallic in color. Like a marble. Clean on your hand, but blue swirl in oil sitting in pan. Now the noise is anytime above 40mph whether your hitting the gas or coasting. Noise is more pronounced when not on the throttle. I was suspecting front axle shaft bearings. The ones inside the front axle. But now you make me wonder. My buddy that looked at it last time said my rear diff had some whine and play in it. But he couldn't hear the noise when driving it. Now the noise is louder. Last time I changed the rear diff fluid was in February or March of this year. The noise I swear is coming from the front like you said you thought yours was. Also when I switch to four wheel drive noise is louder when on the throttle and quieter when coasting.