I know there are a good amount of CX500 owners that follow this blog, so I'd like to share this wealth of information. I'm pretty sure the cam chain or tensioner went on the CX last night. It still runs, so I'm hoping the damage isn't too significant.
Regarding the issue, I was linked to a post titled, The Triple Bypass thread, by a fellow member of CX500Forums.com.
It's a running list of part numbers with the associated items that should be replaced when heart-surgery-style issues arise. If you've got a CX, I'd recommend bookmarking it.