Never heard a rattle as you mention until my former D2 actually started having focus problems. Sometimes it would focus fine, other times it wouldn't. Eventually it became more often a problem than not, and then eventually it stopped focusing altogether. I found out during its period of partial failure that if I tapped on the front of the phone gently right behind the camera it would focus closer and closer on items nearby, and if I tapped on the back of the phone right next to the lens it would focus on distant objects, so for a while I was doing that to take pictures, (sad, I know...)
I eventually found a used camera for the D2 on eBay, and then also found another person selling a complete set of decals for the phone (the back covers) and with it they were supplying the Torx drivers needed to completely open the phone. I paid in total about $30 for everything. Then I followed a Youtube video and a photo gallery of a teardown of the D2 and was able to successfully replace the camera. :icon_ banana: It now focuses and takes beautiful pictures again!
It will now be my son's phone. That wasn't meant to be off-topic, but instead to alert you to the issue, so that if the camera is loose, it may be the start of the same problem I had with the D2. Hope not for your sake, but you never know until you know.