I never noticed Surly cogs being abnormally loud, however I did have the same experience as the OP with a Surly cog. I let the chain wear well past 12 1/16" and when I installed a new chain it was too late. The cog was worn and was abnormally loud and "crunching" especially when cranking hard with a new chain. I don't think the Surly cog is at fault. I've seen the same thing happen with other cogs. The problem was letting the chain wear too long, which accelerated the wear of the cog teeth. I normally get 1-2 thousand miles out of a chain before it needs replacement (when 12 links = 12 1/16"). However, I have worn out good quality chains in less than 400 miles...it depends on the conditions you are riding in and how clean you keep your DT. SS/FG chains are so cheap and easy to replace, its not worth being a hyper-meticulous chain Nazi to squeeze a few extra miles out of it. Just monitor the "stretch" so you can replace it at the right time.