The most common reason for a noise on bumps is a loose fitting rear brake disc. Mine doesn't but I rarely use my rear brake. You can check yours for looseness (and maybe get it replaced under warranty), but I'm not sure you can tell by just trying to move it. You might need to remove the caliper first to see how loose it is. It's a free floating type, but shouldn't rattle.
Maybe someone who's had this problem will chime in.
It could also be a loose side stand, try taping it in place once up (might need 2 people to do this), and take a few bumps you've heard the noise on.
I hope you find the cause.
Mine has the same rattle, however if I am applying any rear brake when I go over the same bumps, there is no rattle. I have taken mine to the dealer purchased from and was told nothing the matter. In fact when I complained about the brake squealling, was told to use the front brake instead?!?! I took it last Friday to my local dealer, sevice tech looked at it, and said "Oh My, that is loose". Took down my info and called the district service rep. They called me back and said Suzuki would not do anything about it, out of factory warranty, if it had still been in warranty they would have replaced it? Said it was not a safety issue, just a nuisance noise? I have one more dealer within close distance, going to try them in a couple of weeks to see if they will do anything? Assume I will have to spend my money and take care of it?
The back of bike doesnt rattle but I get an irritating clunking noise coming from ???? underneath ??? not sure where in the hell the source is. I checked the side stand and rear rotor and found nothing loose. Doesnt seem to cause any porblems and the dealership was less than helpful so I just try to ignore it. Usually only felt on bumps or extremely rough pavement (lots of that out here in the desert)