You should be ok with taking the 6 screws out of the back and gently pulling the back cover off to look for anything loose. The manual even says you can, and you should, to adjust the tension of the sticks to your liking. This is not going to affect the warranty as long as you dont go crazy on it. But i would definitly take it apart just to have a look - BEFORE YOU TURN IT ON!!!! If its just a screw that came loose, you dont want it rolling on the circuit board when you turn it on. And for giggles, go ahead and check the battery compartment before taking it apart. Its easier to take the batt. cover off than taking 6 screws out. I have a DX7 and there is no rattling, just a really soft buzz from the speaker, barely noticable, and it works flawlessly.