maybe you dislodged them when you removed the old drive.
However, if all is working well, do not worry too much about the missing pads.
If here is room, and you have the inclination, you could try to put them back but that is entirely up to you
I have a black Macboook with 80 GB hardrive. I recently undertook to replace it with a 500 GB hardrive which seemed easy to do. However I notice that the new hardrive would not slide inside the machine as there were some interference with two rubber paddings used on the original old hardrive. I had to open the keyboard and the back of the machine, remove these two rubber pads and installed the new hard drive, and screwed the machine back after laboring for about an hour.The machine is working fine with no noise or vibration. Could you or any of your readers tell me any downside of not having these rubber pads? Do I need to stick them back in the hard drive cavity? I think this is a poor design and am surprised that Apple went for it. Regards, Rajan Ramaswami