I just recently experienced this same symptom, although our causes may be different. In my case, the slide bolts had come loose and fallen out on my front left tire! My caliper wasn't being held in place when I applied the breaks and was wobbling around on my rotor (thankfully, I caught it before it caused any damage). I bought new bolts and pins, lubed up the pins and made sure the bolts were on there nice and tight. It's been 2 weeks and I haven't experienced any more problems... *fingers crossed*
Most common cause would be a loose brake caliper mounting bolts.
Typically, a knocking noise when to use your brakes in the car is caused by your brakes wearing down. This means you need to get them checked out and repaired.
Cause low pressure oil pump
If the rear brakes are drum brakes, then there could be a leaky wheel cylinder. The wetness inside the drum will cover all the brake shoes and parts and cause the wheel to lock up when applied. The build of pressure could be due to the wheel cylinder leaking and causing a pressure loss, but rising when the brakes are applied or pumped up. This may/may not be your case, but definitely worth checking the rears.
This is probably due to worn brake rotors on the brakes, if there is no vibration when driving then this will be the cause.
worn brakes could be the cause or check the A frame bushings
No you lose air pressure .
Friction
The most common cause of lifters knocking is low oil pressure.
Vibration when applying brakes is most likely warped rotors. Another cause could be loose caliper bolts.
Usually, a loss of pressure in your brake system means that there is a hole somewhere in the system. A leaking brake line or a punctured reservoir could cause a loss of pressure. A bad master cylinder could also cause a loss of pressure in the back brakes.
Your vehicle is equipped with abs and anti lock brakes, when applied hard enough the system interprets it as a panic stop and pulses the brakes to prevent lock up and skidding.