Worn out wheel bearing will make a noisy sound, like a humming sound. Sometimes it is difficult to find which wheel has a worn out bearing.
One way to find a worn wheel bearing is to rock the wheel by hand. Jack up the wheel, grab the top and bottom (12 and 6 o'clock) of the tire by hand, then rock the tire. If the wheel moves like wheel nuts loose, it has excessive end play. possibility of bearing worn out.
But in this case, there is no wheel with excessive end play found. So the bearing is tested by rotating the wheel directly by hand, after the wheel is jacked up.
This vehicle has FWD (Front Wheel Drive) system. So the rear wheels can be easily rotated by hand. The test results indicate that the left rear wheel has a worn out bearing, because it is humming when rotated.
In the video above, the bearing produces humming sound at a speed of about 70 km per hour, before being repaired. Then the humming sound disappears after being repaired, when tested at the same speed.
The video also shows the left rear wheel being rotated. It produces humming sound, before it is repaired. Once fixed the humming sound disappears, and the wheel rotates more slowly due to the tighter new bearing.
Today wheel bearing is also equipped with magnetic ring to determine the speed of the wheel for ABS (Anti-lock Braking System). And many manufacturers make these bearings. So it needs a practical way to test the strength of magnetic ring before buying it. The following video shows how to test magnetic ring easily.
Sometimes the sound of the tire can also make confusing. By jacking up the tire, and turning them by hand, it can be distinguished whether the noise is coming from the tire or from the bearing. After being jacked up, and the wheel is not noisy when rotated by hand. It means the noise is coming from the tire, not from the bearing.
A worn out tire tends to make a humming sound. For sedan car, moving the worn out tire from the front to the rear can reduce the humming noise.
In addition, the front wheel bearings are also equipped with magnetic rings. The video below shows another way to test the magnetic ring.