Vauxhall Agila

No dials working even though lit up . Occasionally will work ( about once every few weeks)

When engine switch of after about 3 hours a loud chick sounds starts under the bonnet near the battery I have to disconnect battery to stop noise can anyone tell me how to fix it

My coolant is just gone in short journeys , heater is freezing , I can't see the leak but it sounds like a Pressure cooker when I drive for ten minutes

Only does it when ease off accelerator, when foot down no noise, when clutch in no noise, or if put in neutral and coast no noise, no problem selecting gears and no loss of power

On digital display