Expansion tank boiled over, water leaks

about a month ago all the coolant boiled over out the expansion tank i initially thought head gasket had blown however after letting engine go cold and refilling with coolant evrything appeared normal, i let car tick over for an hr or so , fan kicked in and all was normal, oil clean water clean no bubbles etc, ive done a 1000 miles since then oil still clean etc levels good no problems. yesturday i drained all the coolant out and flushed system , i did this as wasnt sure of how much antifreeze was in system because of last months problem and its getting cold, i refilled coolant,let car tick over about an hour got any air out etc and went for a good drive with no problems, got to work this morning steam and water coming from water pump and a chirping noise, whats going on? is this related to earlier problem? is this because i changed coolant? could pump have been bad a while? any help many thanks