Volvo V40 Fault

Track of the day Volvo - Today's Volvo Fault.

Help! Volvo is making a strange noise. It's coming from under the bonnet from somewhere round the battery. I thought it was telling me that the battery was flat. The noise is there when the engine is turned off. The engine won't fire which seems to prove the battery is pretty flat so the charger is now connected up but the clicking is still going on. There's a box under the battery marked 'siren'. Could the clicking be alarm related? Anyone expert in Volvo V40 faults out there?

Update

It's alarm related. Lock the car with the remote key and the indicator lights keep flashing. Activate the central locking manually by turning the key and the doors lock but the indicators don't keep flashing but the alarm isn't set. Meanwhile the car sits in the driveway ticking away merrily, even though the ignition is switched off. It's something to do with the alarm circuitry but I've looked at the fuses and can't see a problem there. It will be expensive.