Recently had my number one road bike serviced at lbs prior to summer(?) 'season' and had rear cassette changed and longer rear mech fitted in a hope it'll give me a better chance at climbing those bloomin hill things First ride, pro service the chain was slapping against chain stay, mainly in big ring settings. Took it back and was told about a 'spring' that was weak, adjustments made and told there should be no more probs. On the whole there isn't but occasionally I'm still getting a bit of slap, large ring - small gear. Any thoughts as to what might be causing this minor inconvenience and how it might be rectified? Many thanks.