Before my appointment, I inspected all of the 3GSs on display and they ALL had the rattle if you tapped on it. Because of that, I deemed it to be normal and it was nothing to be worried about. Due to the fact that the noise goes away while the camera is actively focusing, I'm pretty sure its the auto-focus mechanism.
So.... the genius at the apple store tried to pass it off as the vibrating weight. Psh... i knew better than that so I just said uh huh... ok... ok... politely of course. I had no drive to pursue the internal rattle at this time since all of the 3GSs on display had it.
I moved onto the issue of the loose vibrate switch. I noticed that all of the WHITE ones had a loose switch in silent mode while the BLACK ones still had just a bit of play. I actually got to deal with the manager since my original genius went out for lunch in the middle of helping me. Before that, though, the original genius took my phone into the back saying he was going to take it apart and noticed that it was, in fact, my silent switch that was loose. He swapped it out for another white 32 gig.
Guess what... IT WAS EVEN WORSE THAN MY ORIGINAL!
After I pointed that out to him, he told me to come and check out the display phones. I pointed out that the black ones had a lot less play. He agreed and I asked about switching colors. Black or white doesn't really matter to me. He said that I would have to wait in line for that... which later I found out was total BS. This is when he went out for lunch and he told the manager to help me after he finished up with his current customer.
Finally, I deal with the manager. After rattling my phone next to his ear, he agreed that the noise was indeed odd. He takes my phone back for what seemed to be around 10-15 minutes. He comes back with another worker and he tells me that I threw him in a loop. The other worker tries to explain to me that the noise was coming from the "shake to shuffle" feature and that all the 3GSs had this rattle. Dumbfounded, I told them that I realized that all of them had this internal rattle. I was actually complaining about the silent switch being loose. They then drop their claims and return to the back.
The original genius i dealt with informed the manager that the black ones seemed to have less play and my request to get a black iphone due to that fact. After waiting a little while longer, the manager comes back with a BLACK iPhone. He tells me "It looks like you're not leaving here with a white iphone today. All of the white ones have a loose silent switch when in silent mode." He suggested that the white phones were made on a different assembly line than the black ones, and that there was probably a deviation in the white assembly line which is pretty logical. All I did was sign identical paperwork when doing my white to white switch.
Long story short, I now have a Black 32G 3GS. There is still a little play in the silent switch while on silent, but not so much as to cause an audible rattle by itself. It still has the internal rattle by the camera. This is probably as good as it's gonna get.
By the way, all the phones I got were white box phones with 8XXX serial numbers, so they were brand new phones.