Chain rattle in only one rear ring.
 

2007 Veloce 10 speed.

When my chain is in the 4th rear ring from the top - whether I'm in the big or small ring up front - I'm getting some chain rattle, as if that one particular ring needs to be dialed in slightly somehow. But I can't replicate the noise off the bike, and everything else seems to be adjusted just fine.

Might this be caused by something other than cable adjustment? I've looked to see if the ring is slightly bent or something, but can't see anything.

Thanks.