The �ticks� you are hearing are almost certainly due to thermal expansion (or more likely contraction) due to heating/cooling of the radiator � which is perfectly normal.
The same noise can occur on heating radiators in your home, when they heat up or cool down.
The ticking comes from the cooper pipe that feeds the radiator, if it is touching the joists under the floor boards, normally the installers would rap lagging round the pipes to stop this, its nothing to worry about, but can drive you nuts.