I found the 74gb Raptors to be no louder than the 36gb ones. The 150 drives however seem to me to be a liitle louder when seeking.
It all depends what you're used to though. To me the noise is not an issue, but If you're going from say a couple of spinpoints to raptors then you could well think they are loud.
I have 2 installed in raid 0 with Vista, and they do seem to chatter for a good few minutes after boot, but I think this is due to Vista rather that the raptors.