The forming of air pockets within home radiators will usually be responsible for the sound of running or dripping water emerging from them. Although radiators usually require water to generate heat, it shouldn’t make a noticeable sound, so this usually means trapped air is preventing the water from travelling around the pipes properly.
Typically, bleeding a radiator can fix the issue of radiators making a running water noise. Make sure that all the trapped air is released so that a steady flow of water can travel through the rad pipes.
For further information, take a look at our dedicated blogs, How To Cure A Noisy Central Heating System, and Noisy Radiators: Diagnostics and Cures.