Towel rails, particularly heated towel radiators, can produce a ticking sound due to the expansion and contraction of metal elements when they heat up or cool down. When the radiator heats up the metal components expand; when it cools down they shrink. This shift in size might cause the metal to scrape against mounting brackets or other components, resulting in a ticking or creaking sounds. This is a routine process and not usually cause for alarm. However if the noise is considerable it may suggest that the towel rail is too tightly fastened; adjusting the mounting points slightly can help lessen the noise.