Ahh yes of course, the standard water pump uses a plastic fan which is very well known to, and common to break. The replacement ones, or the only ones that are now available have a metal fan. These only cost about £30. Worth doing if never done before, just so you know its not going to break....but yeah, could well be the bearings on the water pump if its still the orignal plastic fan.
If its not the bearings then it could be a sign that its on its way out and not spinning properly. This of course can lead to overheating.