Hi, I read this entire post and only saw one person that mentioned they are experiencing this problem when the phone vibrates. All others mentioned when they tap or shake. I can't believe more people are not commenting on the rattle caused by vibration. I keep my phone on my desk next to my side all day, and this has been bothering the hell out of me. The marble clanking sound is the most noticable at the beginning and end of a vibrating sequence. Still not sure if I want to bring it back due to the pervasive nature of this.
What I learned through all of this is not to just accept the rattle for normal. I finally brought it in after it was annoying me beyond belief. The consensus was that something was not right with my vibration motor and it was causing the more than normal noises I was experiencing. I got a brand new one and although it rattles, I am not hearing what I was hearing before (the noticeable marble clank at the beginning and end of a vibration sequence).