Recently my chain has been going insane, smacking around and making a bunch of noise. I have lizard skins on my chainstay so it is not just normal noise. This happens even when going over small changes in elevation, say in the sidewalk. I thought it was just due to lateral chain travel, and the chain getting hooked on the knobs of my tires (new panaracer fr's, which are 2.4s versus the 2.2's I used to run). However, I did a quick check of my chain wear by measuring 12 links, and I think it's over the recomended length by 1/8th which probably means I should replace it. Buuut, could the slapping be caused by a worn out spring in my derailleur? I would hate to buy a chain when I can simply replace a spring, although I should anyway I suppose. The bike is about 1.5 years old, with a good solid year of riding everyday to class, and also a fair amount of trail use maybe 1-2 weekly. Generally how long does it take a stock chain to wear out?