Rear Drums Knocking after repair

[monkeyhand]

Hello,

I just had my brakes fixed on my 2000 Elantra and now there is a knocking coming from the rear of my car when I firmly apply the brakes, no knocking before. Here is what they put on my bill concerning the back brakes- Rear Shoes and Turn Drums, Rear Wheel Cylinder (both). I poked around others sites and they implied the drums may be warped. I called up the mechanic and he said that the drums were rust covered and they had to remove the rust, he said they should have been replaced even though the main mechanic asked the guy I talked to on the phone if anything else needed to be done before giving me back my keys. I don't know how they missed the noise if they test drove it. They charged me for 1.2 hours of work to replace the shoes and turn the drums. How much more labor would be involved to replace the drums? Should I go to someone else? Could they have warped the drums when they turned them?

thanks!