There's really only 2 things that happen when you activate the group switches. a) the group solenoid valve is energised and b) the electric motor that drives the water pump is activated, and the water pump turns (if it's not seized or seizing). The sound you describe could be the water pump squeaking / squealing, which could indicate the water pump is on the way out. Watch the water pressure guage for signs of abnormal pressure indications. Otherwise, without being there to listen to the actual sound.....who knows. Sorry cant be more help but you have to be there. Regardz, FC.
