Alright, well I degreased and relubed the chain as recommended. I'm pretty sure there's less noise now, but it's still there.

Using the rope from crank to seatpost method I removed the cog. Luckily it wasn't stripped, so I did the same thing to get it back on. I'm still going to take it down to my LBS because you guys have scared me enough to do it. I'll have them tighten the lockring while they're at it.

What's the likelyhood of stripping a cog by applying too much force when putting it on? because I was afraid I was going to strip the cog when I put it back on... once it got tight it would take a lot of force for it to move at all, and when it did move it was in little clicks at a time. It reminded me of when a bolt spins around the thread and then clicks back into the thread... But I can't spin the cog anymore so I think that it's probably nice and tight. I'll still let my LBS check it out though.