The first thing I noticed when I purchased my 360 was how loud it was. Apparently, Microsoft was on the job for this one and fixed the issue. Unfortunately, those of us with systems built prior to November 2006 will just have to deal with the noise.
Some of the new units are built using BenQ BAD6038 DCVD-ROM drives instead of the noisy Toshiba-Samsung and Hitachi-LG models current Xbox 360 users own. The new drives load faster and have reduced noise.
Microsoft has not confirmed that all new units will be built with the new drives however. Check out Xbox Scene or the Microsoft website for more information.