I have replaced front brake disc and pads and rear brake pads but still there is horn like noise when the car stop as I applied the brake.Any reason.Kindly assist.

 

did you use mercedes benz rotors and pads. there is nothing that compares to mercedes benz genuine parts all the aftermarket pads and rotors squeal and make noise. do yourself a favor replace them with genuine mb brake parts

 

Tip: The vibration created by friction on the brakepads/brakedisk when applying the brake, makes a "sound" like a high frequency siren. "high pitched /siren type" noice from the front brakes.

By using heat resistant copper grease on the brake caliper piston outer end (the end that faces TOWARDS THE brakepadmetal - NOT ON THE BRAKEPAD FRICTIONFACE ) the noice will dissapear.
A small amount of heatresistant copper grease will often prevent the brakepad to swing in the "pitchtoned frequency".

AND: NOT GREASE ON THE BRAKEPADface-side BUT ON THE CALIPERS PISTON OUTER END THAT PRESSES ON THE METAL SIDE OF THE BRAKEPAD.
Remember If you do`nt understand -do`nt use the trick- We are after all talking brakes.