Once my furnace has reach the desire temp and the gas shuts off and the fan is still running I hear a click noise. Sometimes loud, sometimes not so loud and sometimes not at all. What could that noise be, should I have someone to look at it?

The noise is anyones guess since we are not there to hear it. If the furnace is working properly then I would not consider the clicking an emergency but at some point you may want to have a service person look into it. Also since it does not click all the time it is considered intermittent and very hard to find if is not making the noise when the service person is there.