Hi guys, thanks for all your replies. Sorry I didn't get back to you, I've been away for a wile.
So the bike has had pretty much every bit of basic maintenance done to it. (Oil, oil filter, chain tension plus clean and lubed.) I'm still not convinced the bike is sounding as it should. I've noticed that the lloud gear change sound seems to happen once I've been riding for about 10-15 minuets and it's had a good warm up. I've also noticed that I can hear a rattling sound that comes when warmed up too. This new sound doesn't sound like a engine nock or tap but more of a loud rattley chain and only on acceleration. I'm quite sure this sound isn't coming from the main chain but who knows. I've had a look in YouTube and there doesn't seem to be any videos replicating this sound and I'm not sure how to record it myself as it only happens when riding and accelerating. Cheers guys