Boro8688

For the age and miles on the vehicle it wouldnt be uncommon for the noise to be coming from the clutch, The citigo gearbox/clutches are nothing fancy, basic and cheap. I would suggest getting prices from local indy garages if possible, The job itself is straight forward and the price difference between main dealer and auto parts company are massive for the clutch kit. Just price up a kit such as valeo or LUK.

is that when trying to carry out a forced regen?

As mentioned above, It wont be the dual mass fly wheel (DMF) as no citigo has one fitted. so it rules that out as the problem Citigo's do have a clicking noise when operating clutch from engine/gearbox area but this isn't a fault. It does seem strange that its happening only in 2nd gear.

the coolant pump is run separate from the timing belt and is on the gearbox side of engine, The most common cause of coolant leak from that area is the coolant pump housing rubber seal leaking.

Coolant pump housing seal will probably be leaking, To change housing you need to remove the coolant pump belt also. If you replace the full housing you need to change the belt also.