After riding (and falling) through some heavy mud, a couple miles later it was like my rear wheel was just locked up, checked the chain and it was as stiff as a dead snake. So, loosened the wheel, kicked it forward, freeplay was restored. Guys told me, "you've gotta warped chain, change it and the sprockets". So, gotta new chain, new sprockets and pulled off the rear tire and getting ready to go. But, being a noob, I'm curious the old chain seems ok. What does a "warped chain" look like? Is it obvious? What else should I do, since I've got this wheel off and ready to pull sprockets?