My bike has a triple front. When pedalling in the middle chainring on the front there is a scraping sound. The chain is rubbing on the derailer on the side closest to the bike (inner side). Interestingly it rubs the most when the rear is in the middle few gears and not at either particular extreme? At slow pedalling it barely rubs but when the speed comes up and it seems to start rubbing more (if that's possible?).
The high (big) and low (small) chainrings are fine in all but the most extreme gear (no rubbing, no resistance, easy, smooth quick changing).
I've tried fiddling with the shifting limit screws (high/low) as per the Barnett manual and managed the make the low/high shifting a bit smoother but found it made almost no difference to the middle chain ring.
I've checked the chain length etc, all looks good to me. The bike itself is only a few months old...
Is there something else I should be adjusting or checking?
Thanks for your advice. If it's nothing easy I think I'll drop it into the LBS and try and learn a thing or two