Do you have another K5 you can run on the box to eliminate either the handpiece or the control as the source of the problem? Those control boxes have magnets that can slip out of place and it's a similar noise, although the 5 second intervals is odd. From your post, it sounds like the noise is coming from the handpiece and not the box, so this may not even be applicable for your problem.
Have you contacted Kavo yet? If it's new and under warranty, I would recommend bringing it to their attention and see what they'll do.
The tech here that specializes in Kavo is gone for the day, but you're welcome to call on Monday and pick his brain if you'd like - just ask for Rob.
Hope that's a little helpful!
Rebekah