Are the derailleur and the shifter and cassette of the same brand?...
Thanks for the advice guys. I took the gear cable out and looked at all the housings and one was really badly cut with the metal wires bent over the hole. The guy I bought it off said something about adjusting the gears and obviously didn't do a brilliant job. Anyway, I cleaned it all up and fitted a new derailleur as the old one's cage was bent (and for £15 it seemed easier to just get a new one) and shifts are so much better now! Some fine-tuning to be done still but it changes with one click either way now without too much noise either. Just wanted to say thanks for the help and let you know how I got on.
Thanks for the advice guys. I took the gear cable out and looked at all the housings and one was really badly cut with the metal wires bent over the hole. The guy I bought it off said something about adjusting the gears and obviously didn't do a brilliant job. Anyway, I cleaned it all up and fitted a new derailleur as the old one's cage was bent (and for £15 it seemed easier to just get a new one) and shifts are so much better now! Some fine-tuning to be done still but it changes with one click either way now without too much noise either. Just wanted to say thanks for the help and let you know how I got on.