I replaced the front pads, but not the rotors. They still looked good, but I have not seen new rotors to compare too. But the surface of the rotors were very clean, and not grooved or anything.

Whenever I put the brakes on, once it comes to a near stop, or I lightly let off the front brakes, the brakes groan a bit.

Anything to do to fix that?
Their shouldn't be any air in the system and it stops fine.