If your vehicle is showing knocking noise from under the car that matches the speed of the wheels, here are the most likely causes and the parts you'll need to fix each one.
If the wheels were recently removed for service, the lug nuts may not have been tightened properly. The wheel wobbles on the hub as you drive, creating a rhythmic knocking sound that is highly dangerous.
The constant velocity (CV) joints on the axles wear out over time, especially if the protective rubber boot tears and lets dirt in. This causes a heavy clicking or knocking noise that matches wheel speed, and is usually much louder when turning.
A large bolt, rock, or a bulge from internal tread separation will strike the pavement once per revolution. This causes a thumping or knocking noise that scales perfectly with the speed of the car.
On rear-wheel or four-wheel drive vehicles, a failing U-joint on the driveshaft will bind and clunk rhythmically as it rotates. Because the driveshaft spins proportionally to the wheels, the knock matches your speed.
If brake caliper bolts are left loose after a brake job, or anti-rattle clips are missing, the brake components can shift and knock against the inside of the wheel or the rotor once per revolution.
While wheel bearings usually produce a humming or growling noise when failing, a severely destroyed bearing can cause the wheel hub to shift excessively, resulting in a rotational knock or clunk.