whistling squeaking noise

[tommygough]

hi i have a 98 yamaha beams engined celica there is a whistling or squeaking noise coming fron engine bay which increases in speed under acceleration but doesnt really get any louder.noise is really bad in cold mornings or wet conditions but gradually decreases as engine gets warm but could take fifteen mins to disappear at first i just thought it was fan belt squeal but now i think its maybe a bearing noise also e.g. water pump or alternatar it seems to be coming from alternatar but cant be sure because timing belt and water pump are all in close proximity im wondering does any one know a way of determining which off these it actually might be and if not which order would be best to start replacing fixing etc. thanks for any help