I fitted a Dimplex Quantum heater!

danrv

rickendude said:

The clicks basically happen roughly at a rate of 1-2 clicks per second(!), it drives us nuts and happens whenever the unit is active. we both hear it from the 2nd floor.

Does it happen during the seven hours it's charging?
If the clicking is constant when active, it doesn't sound like the normal expansion noises that can naturally occur with heaters.
Might be a relay or the fan as mentioned. 
The Quantum should be quiet during operation so that would be down to a manufacturing/design fault. 
I'd get the heater replaced under warranty if it can't be fixed.