I removed the bike chain and wheels to clean them but when I put it all back together I noticed the rear derailler arm isn't as vertical as before. It's actually so horizontal that the chain rubs against itself when using the smallest cog.
It seems like the chain is too long because if I pull it toward the front derailleur the rear arm goes into it's natural position. Problem is, I didn't change the chain. I checked and double checked how the chain is threaded through the derailleur and can't imagine it working any way other than how I have it.
It also didn't shift right going to the smallest cog when I rode it but if I flip the bike over and shift all the gears it works fine.