I found the following link talking about how the 360 can scratch discs if moved while on. Here is the link, but the part at the bottom is what may help you out:
http://www.llamma.com/xbox360/news/Xbox ... atched.htmAt the bottom of the page, the last comment was this:
**Edit 12/04/05 **
I think we should also acknowledge that some users are experiencing scratched discs without moving their console. We have received some direct feedback from a at least two people. I imagine the vast majority are due to moving the console but the mechanics of the problem is the same. The disc spins very close to the pickup and the tray does not prevent the disc from reaching the laser pickup. If you are experiencing scratched discs without moving your console you should contact 1-800-4MYXBOX for warranty support from Microsoft.
-LlammaPerhaps if you called that number, maybe tell them that your disc was scratched for no reason at all MYSTERIOUSLY and see if they can get them replaced. If you have more than one disc it may sound peculiar to them that both were scratched for no reason so maybe you could wait before calling in the 2nd one or perhaps have someone else make the call to replace the 2nd disc.