The ticking sound may just be metal parts cooling off. This happens when metal expands when heated, and when the metal cools, it contracts, and many times there can be a noise like this as the metal cools. It may be in contact with something else that isn't moving and that is where the noise comes from. If the unit is working, I would not worry about it, and you will get used to the noise. It's kind of like people worrying about the water pump making noise, I just think, as long as the pump is making noise, it's working, and I'm happy