I am new to biking. I just bought an used Trek 6500. The only problem is that in certain gears it seems that the chain is skipping. What I think it seems to be is one of the derailleurs is not positioned completely right so in certain gears the chain is hitting the derailleur and it is almost trying to switch gears when it isn't supposed to.
Is this a common problem? Is it difficult to adjust the derailleurs? Any advice would be great.