During braking, the brakes make a grinding sound.
The reason why brakes make a grinding sound
(1) Excessively worn brake linings.
The brake linings are worn down to the metal and they are rubbing against the disc or drum (i.e. depending on if grinding is coming from front or rear) when you apply the brakes; this results in the grinding sound you are hearing. In other words, they are worn to the bone, there is nothing left, and they have been neglected too long.
What to do?
The car's brakes have been neglected and as a result, it could be expensive to fix. First, you'll need a new brake lining. Second, you'll need to at least have the brake discs or drums (i.e. depending on if grinding is coming from front or rear) machined in order to smooth out the damage done by the grinding. If the damage is extreme, the mechanic may suggest new discs or drums (i.e. again, depending on if grinding is coming from the front or rear).
