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
When rainwater gets on brake pads, it can cause them to vibrate and make a squeaking noise when the brakes are applied.
No you lose air pressure .
The most common cause of lifters knocking is low oil pressure.
Friction
Vibration when applying brakes is most likely warped rotors. Another cause could be loose caliper bolts.
A knocking noise when coasting in a vehicle could be caused by issues with the engine, transmission, suspension, or brakes. It is important to have a mechanic inspect the vehicle to determine the exact cause of the noise.