... is this normal? (3GS white 32GB)
It only happens sometimes. Someone with a 3GS: try shaking the phone slowly.
The problem has already been diagnosed. Read your own thread, please. We've done as much as we can through the interwebs.
How do you know that this is the problem though? I had a similar problem with my 3G, where I could hear something rattling inside, but only sometimes. It would cause the phone to randomly lock or turn the volume up/down. I got it replaced.
Perhaps it is just the camera, as I haven't played with a 3GS, and haven't been able to shake one, but you shouldn't say that it's nothing as a fact, as there could be something wrong.