My 2003 Ford Taurus, which I bought with only 30,000 miles on it in mint condition last October has been giving me some trouble. It felt like the brakes were going, and took it to several mechanics, and finally picked one and had the rear drums and shoes replaced. Now when I brake hard I hear a knocking sounds–not sure what it is???
Take the car back to the mechanic who replaced those rear brake shoes. Most likely he did not do a thorough job and failed to secure something.
I went back, he changes the rear drums and shoes…drove away with no sound, until it came back again 20 mins later. That same knocking sound is back.
You may want to have the front brakes inspected.
The brake pads have some sort retainers that hold them firmly in the calipers. If these retainers are weak/damaged in any way, it can cause the brake pad to move where it comes in contact with the caliper. So as the rotor comes around, it grabs the brake pad and bangs it into the caliper and then the pad bounces off only to be repeated each time the rotor comes around.
The reason why it may take a while of driving before this occurs is, as the brakes are used they heat up the calipers. And when things heat up they expand, and this may provide enough clearance for the loose/worn pad retainers to allow the pads to come in contact with the calipers.