About 2 months ago I bought an X51. I currently live in Costa Rica. About a mont ago, I began hearing a strange noise once in a while coming from the graphics card section. This sound only appears after 2 or more hours of constant use, and it's quite audible when the PC is sitting vertical, not quite so when it's layed down on its side. Also, when moving it up from an horizontal to a vertical position the sound is even more audible. I opened up the PC several times to rearrange the GPU cable, thinking it might be touching somehow the GPU fan, but it hasn't solved the problem.
Anyway, Dell support came and changed the CPU fan (because it was making a rattling noise) and the fan that's back to the Alienware logo, which is right beside the GPU, but the problem persisted. So I wanted to tell my issue in the forum to see if anyone else has experienced it too, so that I can better explain it to Dell support, because at this point my only bet is that somehow the GPU fan is broken. I include a sound recording of the problem so that you can hear it. It's like a brbrbrbr sound.