It's a timer probably for a water heater. The top switch is a bypass for the timer itself. So when the timer wheel has the power off, the switch moved to the "constant" position allows you to turn on the appliance manually. Off is obvious, everything is off. The "Timer" position allows the mechanical switch of the clock wheel to turn the appliance on and off. The noise you are hearing is probably the electric clock unit or as it switches the appliance on and off you are hearing the click of the switch.
If it is a constant noise then it is the clock motor. If you can open it up a few small drops of oil on the gears of the clock mechanism might quite it down.
I cannot tell if the wires are low or line voltage. Since in the UK you have 220v line power your wire size (gauge) can be smaller. Also the age of this device probably makes it a line voltage unit. The wire jackets look like NMC type as we have in North America for full line voltage. The color of the wires is similar to 24v ac controls such as thermostats. Just note there is a big difference in voltage between the two. If you do not know what you have just do not touch the wires with power on.