You need to separate the various aspects that might be causing the noise from each other. Does it rattle only when riding? Only when pedaling VS coasting?

If you're considering a new rim and spokes on the old hub then before you do you should open up the hub bearings and see their condition. Are the axle cones pitted or rough? When the wheel is spinning, secured in the frame without a chain, how does the wheel feel? Place a finger on the axle end and can you sense any vibration/roughness? Then repeat but with the freehub body held still (as in how it is when coasting)?

Rattle is not the usual term used to describe a hub or freehub bearing roughness. Still if you're going to the expense and effort to relace a new rim, the hub's condition should be determined and judged as to it's worthiness. Andy.