You should have it looked at by a qualified Service Center. A "rattle" is something loose inside, you need to have the instrument looked at - it can only get worse if left unattended. If you really are not near an authorized service, you should at least call Yamaha Customer Support and perhaps some one can give you instructions on taking a look yourself. Your description is really worrisome or maybe it is just unclear - when you say you can 'feel Movement' - that is like your instrument is possessed or something.
🙂 What, like something alive and kicking inside?

Paul wrote: I have since found out it wasn't a Fault, since i recently moved my CP4 on the LG800 Stand to the second hole thats the Furtherist away from me i no longer have this problem.

Can you help me i have the Yamaha CP4 and i have an Intermittent problem with it sometimes when i play the B note just below Middle C with G above Middle C i hear a Rattle type sound which i find very annoying it only comes into the piano about twice a week and doesn't last long maybe 5 to 15 minutes i wont have a Year until March 2015 i would hate to have to send it back as its my pride and joy and wouldn't want it to get scored or Damaged,when i place my fingers on the top of the piano i can even feel Movement when this Rattle is present.I hope you can please help me.

So it was possessed! 🙂

Glad you got that sorted out... intermittent problems are the worst but when you described it as a "rattle", ...had to be something easy!