Coming out of CLT tonight we had an phantom RA right after takeoff. It showed a target right on top of us, same altitude with instructions to "monitor vertical speed", then "descend, descend", "descend faster". Needless to say scared the **** outta me and the captain but we were in VMC and nobody within 2 miles of our position. This also happened a couple of weeks back doing a visual approach. Anyone have any idea why this might happen or have this happen to them ?