Due to the thinner plastic and less material used overall, noises that were used to be muffled on the old Original Models and the Slim models are less attenuated.
Either way, there isn't really much you can do to quiet it down, but optical drive noises and hard disk noise is normal.
It also depends on the game you're playing...
Games like COD, sadly, thrash the lens to and fro while playing online.... usually a sign that the game has ZERO hdd caching coded.
Other games like... Uncharted, don't have this issue because the disc itself has duplicate copies of data spread around the disc in order to speed up load times and lessen wear and tear on the BD-ROM drive.
Plus as stated, newer PS3's are a little noisy due to how they are designed.
if you sit far enough away and high enough volume, you'll never notice.