Searched the forums, couldn't find much, so here it is.

So, basically I've been over my rear derailer and looked at everything -- relubed/tightened jockey wheels, replaced the chain with a properly sized new one, readjusted the indexing from scratch. I know I should probably replace the cassette since I changed the chain, but I don't really want to *if* I can help it (due to money/student status).

The problem is that when I am applying pressure to the pedals while riding (not while cranking by hand, oddly) and shift to my fourth gear combination (middle chainring, and just for clarity there's about 18 teeth on the rear sprocket), my chain catches on the lower pulley wheel (ie. it doesn't go between the rollers smoothly and "catches" on the side plate of the chain).

I'm honestly confused. There is a bit of play (a few mm) in the rear derailler's top pivot joint, if that's of any help. Could the bushings be worn on the lower pulley wheel?

BTW, first time poster, long time lurker. You guys rock, hopefully *someone* can help out, heh.