clicking on hammer return

[Bec and John]

Hello,

I have a clicking sound when various hammers return that I can't 
isolate. It happens with the action in or out of the piano. It appears 
to come from around where the hammer hits the "cushion" (I forget what 
that's called) on the hammer stop rail. The hammer doesn't appear to 
hit hard enough to cause a click - I just can't find where it's coming 
from.

Thanks!

- John