Click goes the chain boys, click ... click ... click
Okay, apologies to whichever aussie battler sang the original (shearing song :-)). Had this happen to me on my new bike on a long ride while in the middle of nowhere. Not having a spair chain or any tools to deal with it decided to just keep riding and deal with it when I got back.
On inspection I found an Ultegra 6600 chain with an SRAM quick link and immediately behind that the link had been pinned with what was obviously a nine speed pin. I'm amazed I got as far as I did like this and even more amazed that someone (previous frame owner) would knowingly do this. It's not like it isn't obvious when it's in because it sticks out well past the link plate?
Fortunately I remembered a D/A chain on Craigslist that day so for $30 I now have a shiny new CN-7801 on there.
And the click went away ... :-)