over sixty thousand miles i would or if never replaced you can look for missing teeth in the belt fray areas or slack.A lot depends on driver too if your not rough on the auto and no signs of shredding or belt fraying bits of old belt in the bottom of the cover and money is tight dont replace. But being a mechanic i would suggest you do. The water pump has fins on the inside and a bearing the metallic sound is more than likely the fins contacting the water pump cover. It is alot easier to replace the timeing belt if you are changing the water pump. Most mechanics charge 200 to 250 plus parts I actually changed one on the first of may for 200 plus parts and takes 3 to 4 hours. This older car take to a trusted mechanic not a dealership mitchel is a technical manual that will say 7 hrs time and this is what you are billed for i know our local toyota dealership is 150.00 to look at then 45.50 per hour plus parts and will want to flush radiator and replace thermostat lady 1997 corolla was to cost 1426.00 plus tax through our local toy. dealership Idid it for parts and all 315.00