We measured the noise level of the system while loading the Intel CPU using Prime95 and GTX780M using FurMark. We also recorded the noise level with the system idling at the desktop.
Under general use the laptop remains very quiet, however when you start stressing the processor or graphics card it becomes louder. It's not obnoxiously loud like some gaming laptops, however it's certainly noticeable.
ASUS do some great gaminmg machines too, and they cost a lot less than Alienware, but at least Alienware put a lot of effort into the looks as well, which is important.
Great machine, I own one, been using it now for gaming for a month. runs a bit hot on my knee, so I use it more on a desk.
The problem with Alienware laptops, of which I have had many, is the hinges wear out so soon. If anything needs replacing it is absurd at costs.