When on the middle front and smallest back of a 7-speed I feel a rumbling sensation in the pedals. Things aren't dead quiet either. I hear a pronounced sound of a chain running over sprockets that I don't hear in on the other rear sprockets. I don't think it's my bottom bracket and the chain is new (SRAM PC-58 equiv). I got a steal on my rear deraileur, an RD-6600, which is a Ultegra 10-speed. I am wondering if the wider chain could be rubbing on cage plates where it runs around the lower jockey wheel. I can move the chain back and forth on this jockey wheel allowing it to rub the cage. I don't know if this is normal or not and if I need to replace the jockey wheels. They have 4,000 miles on them and have never been serviced.

The smallest gear could also be worn out. What are the visual clues when it is time to replace a cartridge?When the teeth wear do they 'hook' the chain and slightly wrap it around the sprocet before it is pulled free of the tooth? This may explain the chain/spocket noise I hear when I have the bike in the stand.