I think this rod is the source of my rattle, what is it and how do I tighten it?

[Gilles]

Not sure, but seems that that could be the parking brake cable? Try to wrap a bit of foam, held with with tape to see if that helps?

PS: If this line is metal, it could be the hydraulic line for the rear caliper as well.. if so, check if it's rubbing (no good..) or simply rattling into something else, IF this is the brake line, you may gently bend it a bit (re-shape it) away from where it is touching, good luck!