There have been reports that the UK center for XBOX's is shipping thousands of faulty consoles for repairs
Anywhere from 1,500 to 2,500 consoles are getting sent per day to be repaired. I could not find a definitive explanation as to why they are being sent in.
I would highly recommend you inspect yours closely.
The majority of the XBOX consoles are the ones where the the 12 month warranty has expired.