Rear discs making noise

I recently installed the ZJ rear disc conversion and love it, except for the noise they make when first applying the brakes. It's sort of a loud groaning noise that only happens when going slow, in forward or reverse. Where do you apply the brake grease for discs? Would this fix it?

This may be a dumb question but did you install all new components (pads,calipers,rotors) when you did this?

Yeah, pads and rotors are new. The calipers were supposed to be from a low milage 5.9 ZJ and appear to be in good working order. Has anyone else had a problem with new pads and rotors making a groaning noise under light braking, when you first step on the pedal?

I have the same rear disc setup and love the difference in braking performance. No moaning from day one, all used but pads.
You apply the disc brake grease goop where the pad touches the caliper on the outer and where the pad touches the piston on the inner. The goop will solidify slightly to ensure that the pads don't vibrate or moan when the caliper begins to clamp down on the rotor. It might take care of the moan.
Make sure that you lubricate the slider pins for the calipers also.