I opened my MBP today and was able to fix this metal "clinking" noise. I believe that post at the Apple discussions boards was almost right.
The poster says to just tighten the screws holding in those brackets. But they don't tighten, and I think this is by design. Those brackets are holding clips that clip into aluminum tabs on the inside of the bottom case. It helps with aligning the bottom casing for the 10 screws you have to put it, and it also adds some structural support so that the case doesn't flex in the middle if pushed on. I think this is by design because having a little play makes getting the bottom cover to click into place easier. Since I believe those clips give the bottom more support, I didn't watch to just remove the brackets holding the clips (there'd be nothing for the metal tabs to latch into.) So although that would fix the noise, I don't think it'd be good for structural support of the bottom aluminum sheet.
I figured I'd be able to rig it so that they were in the right spot for the aluminum tabs and didn't move so I could avoid that clinking noise (which is caused by the plastic bracket falling on to the metal screws.)
I looked around my room and found some stuff I could use. I took a thin piece of gray foam that came with my Intel SSD and cut small pieces from it. What I did was remove the brackets, place a small piece of foam between the two screw holes under where the bracket sits, and then screw the bracket in over the foam. Basically, the foam acts as a spacer. I didn't have any washers that small or else I would have used that. I did this for each bracket (there's only two) and it seems to work really well!
It holds the bracket in place, tightly, against the screws so that there's no more movement and no more clinking noise when opening the lid, moving the MBP around, or having it on your lap. I was able to easily "click" the bottom sheet into the clips too.
Here's some pictures.
Here's the two brackets that are causing the noise:
This is just the right bracket. If you touch it with your finger you'll notice it moves quite a bit.
This is a pic of the right bracket removed with a piece of foam in place:
This is the foam I used:
And this is the 'finished product':