I have a 2.0 diesel seat Leon FR. I had the cam belt and water pump changed by a friend about 3 months ago. Not sure if the following are due to this. If noticed a relatively noisy ticking sound at idle. Once I increase the revs to 1000 it disappears. What could this be?

Next issue. In the 5 years I've had the car I've hardly had to top up the coolent. This morning the warning light was on telling me the coolent was low. Seems a bit strange that this has happened a few months after the cam belt and water pump change. My friend did tell me to keep checking the water after he had done the work. Is there anything to worry about?

Edit: Regarding the ticking / knocking sound. I had a full service done at the same time as the cam belt change which included an oil change. I've just put some new oil in which is the correct VW grade and the noise has drastically improved, it just sounds like a normal diesel sound now.