possible bearing problem

while driving my car the other day i herd a high piched whisling sound (a sort of metallic sound) now i was told it could possibly be a bearing which makes sence with the noise i am hearing, but it is really quiet and from under the hood i don't hear it at all nor car i hear it with the window down while driving but from inside the car stopped or moving with the windows up you can hear it and it sounds like it is coming from the driver side of the car, where there are no pulleys or all the accessoris that are on the passenger side of the car, My car is a 2002 SE with a 5Spd and the Zetec and about 75000km if anybody knows anything about this it would be much appricated, also as a side question after how many km are you supposed to change the timing belt? if anyone wants more info ask and i'll tey to provide what i can