Sudden forging

I have a barefoot horse that has started forging all of a sudden. Not always, but I frequently hear those telltale clicks at the walk primarily. It's not from the farrier...there have been no changes in his trims and he's not long. I read somewhere that it can be caused by stifle soreness--but he's been a pasture puff (more or less) for months so I can't see any reason for his stifles to hurt. Can there be any other indicators of sudden forging?

Have any photos to post?

Just because he's been a pasture puff for a while doesn't mean he can't have stifle issues.