I found this speed comparison between HD loading and the traditional DVD loading to be worth reading. Initial findings strongly suggest that a properly optimised game won't benefit much from HD loading. Halo 3 is actually slowed down! Multiplatform and less optimised releases may benefit more.

IGN had a video comparing noise levels. Vaguely intriging at best; it's heavily dependant on your console as some have quieter DVD drives while others have jet engines. I'd link to it but I can't find the page; I got to it via a link from another forum.