At low revs, if I'm quite hard on the throttle the chain starts 'clucking' at me... Like a tapping noise, The tension is alright but I can see that it had worn though it's 'rest' (apologies I'm not sure what this part is called) on the top leg of the chain, where it rests on my swing arm, is is some kind of linear bearing to save wear on the chain and swing arm. where do I get another of these? is it hard to change? what is it called and is it likely to be the underlying factor in this funny noise? I await your useful advice patiently