Knocking Noise

I took my car to a reputable nationally known auto shop for an oil change. They called me shortly after I dropped my car off and said that I needed new brake pads, that my current ones were 80% worn. It sounded very necessary so I gave them authorization to replace my brake pads. Ever since they replaced my pads, I hear and feel and knocking noise when I brake. I have taken it back to them several times. The first time they gave me new roters (sp) (at their expense) and the second time they resurfaced my roters (at their expense). I advised them that I still hear the knocking noise. I took my car back up there last week to get new tires and an oil change and asked them to check out the knocking noise again. They said that they did a brake inspection and a front end inspection and they say that nothing is wrong. I still have the knocking noise. Can someone help me?

I have seen riveted linings break loose and elongate the holes through the pads and the lining would move back and forth. Then there is the chance that they left a bolt out and the caliper is hitting the wheel, but they should have noticed that when the wheel was off. The spacers around the caliper bolts could be missing, so when the brakes are cold enough, try to move the caliper up and down and see if it just clanks about.

Thanks. I am thinking of taking it to a different auto shop and tell them of the knocking noise and let them do an inspection and see what they say.