Moaning brakes
 

It's a 98 ML320 with 65k, the tires have about 5K on them.
The rotors and pads were just replaced.
Initially after the install everything was fine, but then coming down from speed (65mph) and rolling through a toll booth I heard a moan coming from the rear of the vehicle.
It was intermitent while I was rolling at low speed (5-10mph) without my foot on the brake! When I got up to speed it went away. The car brakes fine, does not pull.
This noise is infrequent.
Do the rotors need to be balanced, or re-hung?
Or are they just "breaking" in?
Also... while I have your attention...
My right rear brake light went out, but the bulb is still good... is there a sending unit that needs to be replaced?
Thanks for your help folks.
Regards...
Mike