there is a splined nut inside of the hub which tightens the freehub to the hub. this nut has possibly become loose and is floping around inside the hub. this will also cause wobble in the wheel as the freehub is not tight to the hub itself. you enter in from non drive side to access and tighten this nut. i know this because i had exactly the same problem and it was the nut that holds freehub making all the noise.