It is perfectly normal for domestic radiators to click and creak – it is an occurrence born of the expansion of metal as water flows into the radiator.
Usually, these clicking noises will happen when a central heating system is switched on or off, and should be of no real cause for concern unless the noises begin to audibly alter.
For a more detailed insight, take a look at our dedicated blogs, How To Cure A Noisy Central Heating System, and Noisy Radiators: Diagnostics and Cures.