You know, if it weren't for me just now seeing this thread, I would have said that the cam gears were loose.
Like, seriously, I was just about to post that as my guess.
Well, no internetz points for me tonight. I wish you hadn't have found out yet, just so I could post. How about I post anyway, and we pretend it was yesterday.
Sounds just like a cam gear not being on all the way. Sometimes they can back themselves off a bit after install if you don't torque them down really tight. Always follow torque specs.
Ok done. ^^^ called it. lol