Rattling of a Shimano Nexave roller brake
I have these fitted to my Carrera Subway 8.  

They seem to work well, but yes they rattle quite a bit when going over rough ground.  The cooling fin becomes tight when the brakes are applied so must be a direct connection to one of the friction faces.  

I might have a go a dabbing a bit of silicone at three points around the interface of the cooling fin to see if it subdues the rattling :-)