if it is a clicking or ticking noise it will be expansion of the pipes or radiators as they heat up, rubbing against whatever they contact. This noise will only occur while heating up or cooling down.
Nudge the radiator from side to side while it is clicking and see if the noise stops for a few seconds.
Steel radiators are now always delivered with U-shaped plastic inserts to go between their support strips and the wall brackets, which slide silently. Some ignorant or lazy plumbers do not know what they're for, or don't bother fitting them.
You say you have aluminium radiators, which from memory will expand more. I would hope they also have some kind of silencing inserts. If you ask the manufacturers they will say. To fit inserts the radiator has to come off the wall which is somewhat tiresome but, for a single radiator, can be done without draining the whole system. You would need a plumber. It is not gas work so doesn't need a boiler engineer.
If it is the pipes expanding under the floor, they usually tick faster but only for 15 seconds or so. being small they heat up fast. That would mean taking up the floorboards and shaving away the joists where they rub, or packing in felt to slide on.
If the pipes are in a concrete floor and have not been sleeved, it will be much more difficult.
Another possibility, if you have TRVs, is that they have been fitted the wrong way round, and are chattering against their spring. This only happens when the room is up to temperature and the valve is starting to automatically close. You can detect that because if you turn the valve slightly up, or slightly down, the noise will stop until the room reaches the temperature of the new setting. Modern TRVs are often bidirectional so can easily be fixed.