Humming kind of road sound

Axle shafts cannot make that kind of noise. Ninety nine percent of the time when the noise sounds like an airplane engine and it is still there with new wheel bearings, it is due to improper installation procedures. It is critical that no vehicle weight be placed on the bearing assembly unless the axle nut is torqued to specs, and that spec is uncommonly high on some GM models. A typical torque spec is 180 foot pounds, and must be set with a click-type torque wrench. Some GM's call for 240 foot pounds.

Often do-it-yourselfers and inexperienced mechanics will set the vehicle down on the tire to hold the axle shaft from rotating so they can tighten the axle nuts. At that point the damage has been done and the new bearing will be noisy. Instead, stick a screwdriver through one of the cooling slots in the brake rotor to hold the axle shaft, then tighten the axle nut to specs.

To verify the new bearing is noisy, you can run the truck, in gear, on a hoist, and listen next to it with a stethoscope. You can use a tool called a "Chassis Ear" to identify the cause. That is a set of six microphones you clip to suspect parts, then you switch between them with a switch box while listening with head phones. A third way that works best when you have front coil springs is to raise that tire off the ground, reach over the tire and lightly wrap your fingertips around part of the spring, then slowly spin the tire with your other hand. If that bearing is noisy, you will feel the buzzing-type of vibration in the spring.

I have never seen a torque spec lower than 180 foot pounds, so I looked it up for you, and you are absolutely correct. It calls for 151 foot pounds. If there was never any weight on the bearing while the axle nut was loose, the next thing I would be looking at is tire wear patterns, specifically, "toe" wear. That is caused by the two front wheels steering slightly toward or slightly away from the center of the vehicle while you are driving straight down the road. This will develop a feather-edge pattern that is identical on both tires on that axle. If you look at one block of rubber tire tread, one corner or one side will be raised up, and the other corner or side will be scrubbed down. Your fingertips will slide easily over that tread in one direction, and they will catch on the raised edges in the other direction.

One potential clue to toe wear noise is it changes with changes in road speed, as you observed. If you find this type of wear, the vehicle needs to be aligned, and you have about a fifty percent chance those tires will wear flat again if they are moved to the back, at least if the vehicle has a solid rear axle. If you have independent rear suspension, or if you leave the worn tires in the front, the wear pattern set up now will usually continue to occur until they are worn out. The noise may subside over time, but the wear will usually never totally go away. That is important to keep in mind because if a conscientious mechanic notices the wear in the future, he will likely recommend an alignment. You will have to inform him that was already done.

A lot of people think you must use a c-clamp to retract the piston into the caliper housing, but if you have to resort to that, there is a ring of dirt or rust on the piston and that piston or caliper must be replaced or rebuilt. You probably know that already. This changes though if you have a dual-piston caliper. Pressing in one piston may cause the other one to come out. In that case, use the c-clamp to hold the first one in while you work on the second one. Loosening the cap on the reservoir will make this easier too because you will be moving a lot of fluid.

Calipers and rotors will not make a humming sound. You have to be looking at things that are rotating. Half shafts and the bushings they run on do not rotate fast enough to cause humming noises either. Based on your observation the sound changes with changes in road speed, did you look at the tires?

If you think this is not tire-related, have you heard of or seen the tool called the "Chassis Ear"?

I just bought the original model a couple of weeks ago. I searched and searched for years to find a need to have one of my own. Finally stepped up to a 2014 truck that was smashed at 4,200 miles. My friend has a body shop where he specializes in rebuilding smashed one and two-year-old Dodge trucks for about fifty regular customers in his area. Once he got mine done, it had a tiny buzzing rattle when I lugged the engine a little. Found the skid plate under the transfer case was bent up and just barely rubbing. Straightened that out, and the noise is gone. Darn the bad luck. Now I have no more need for the Chassis Ear. On my old rusty trusty daily driver, if a new noise develops, I just wait a few days for a part to fall off on the highway, then the noise is gone!

Keep me posted on what you find.

Nope. It is meant to be removed when it needs to be serviced. It is customary to mark the yokes so the shafts can be reassembled in the same relationship. Each part of the drive shaft was balanced independently, but on the off-chance some work was done in the past that involved curing a vibration, it's standard procedure to try to put things back together in the same orientation.

No. They do not rotate fast enough to cause a noise.

The tires can make a humming noise if there are scalloped. Here is a guide so you can see what I am talking about:

https://www.2carpros.com/articles/how-car-tires-work

I would rotate the tire from front to back to recheck. Also, if the noise is coming from the front a rear driveshaft will not cause the issue. Can you make a quick video using your phone and upload it here in your response so we can see whats going on? I have seen the trans axle carrier bearing go out causing the noise you are describing as well.

You might need to put the car on a rack with someone inside to run the engine and put the car in gear to pin point the noise.

Please run down this guide and report back.

Cheers, Ken

The rear shaft will turn while moving as it is how the AWD system keeps the drive line in sync in the event it needs the extra traction. I would not remove it and leave it out because that can set codes due to the rear axle not being powered. A bad carrier bearing could easily cause noises if it is allowing the shaft to move out of proper alignment.

That lock the rear differential and the front drive together so it is either inside the axle or the shaft has a failed joint. You could bob the shaft out for testing. Move the joints around and see if one or more are stiff or notchy. Replace the carrier bearing if you feel it is bad.