grunting brakes

[cx009]

need your advice. from stop while my gear on drive, whenever I let go the brake pedal (from mid to last few cm) I hear this annoying grunting. I had a corolla before and same problem appeared but only during after I wash the wheels, and it stops/disappears after few minutes of driving. With my 3, it's been >6mos now. Luckily, haven't had no trouble, brakes still strong.

 

[sunrun176]

Do you mean that they "grunt" just as the car sloooowly moves forward at the limit of the brakes holding the car from moving as you gently lift your foot from the brake pedal? If so, I'd say that's fairly normal when you lift your foot very slowly from the brake pedal and it shouldn't do it much (if at all) if you lift your foot quickly.

What's happening is that the pads are exhibiting "stiction" (the friction that tends to prevent stationary surfaces from being set in motion) which causes them to alternately stick and then slip rapidly and repeatedly which in turn causes a grunting or groaning sound. If it were occurring at a higher frequency it might sound like a low hum. It's the same sort of thing that happens if you dip your finger in water and then rub it around the rim of a wine glass. Every car I've ever driven makes this sound when the brakes are at the limit of grip on the rotors at a dead stop and my wife absolutely hates it when I do it on purpose. (lol2)