I haven't personally but know people who have. M$ send it back unrepaired and ban the console and GT from Live forever.
Martin88 posted a topic asking about what he needs to perform the x-clamp method, it has links to the guides to perform the fix yourself.
The topic is in other consoles and called XBox 360 X-Clamp Replacement, What's the best method? (can't link it).
If you don't feel like attempting the fix yourself, can you ask whoever you got to flash the 360 to do it? (it's pretty simple).
Only other suggestion is to reflash the drive with your original stock firmware, providing you have it backed up that is, and your warranty sticker is intact. This makes the 360 back to how it was when it was purchased, so M$ would fix it for free.