Need more detail -

Is the clicking very frequent, such as would be caused by each link in the chain, or is it less frequent?

Is the clicking sound (apart from other sounds) about the same in all gear combinations?

If not, which combination of front (large/middle/small) and rear (largest/smallest) does it occur?

**When did it start and did anything happen to the bike or was anything done (maintained or replaced) at or before that time?