Very easy to take the cluster out. Just make sure you disconnect the battery as the back of the cluster is all circuit board, one live wire and POP! (Been there).
And the yellow plug at the back that you have to disconnect has a locking latch on the side of it. You can see it if you leave it for last and pull out the cluster most of the way. Oh, also you may scratch the top of the steering wheel neck if you pull out the cluster too aggressively (Been there too.)

Not too sure what's back there to rattle tho'... Something could have dropped in the heat vents - or the back of your head unit area could be the culprit too...

Good Luck.