Whirring/grinding noise under hood

[Honkanen89]

Ok so I have a 98 Buick Century, which has given me its fair share of problems but I still love it, and ever since I had the car I noticed a weird sort of whirring or faint grinding noise coming from the engine area somewhere but I didnt much pay attention to it until I brough it to a shop for a front end inspection and they told me that they dont deal with engines but it sounded like I had a bearing going somewhere under there, quite a few people have said it sounded like a bearing was getting ready to quit on me. I took it to the mechanics teacher at my high school and he brought out a mechanics stethoscope and listened to a couple things and then told me he thought it was my A/C pulley. He had to go do something else so I listened to that and a few other things but I noticed no difference in sound.... Reading online it sounds to me like it could very well be my alternator. But before I do the only thing I could think of and take off the belt and see if it spins rough or has play I decided to check with the experts here and see if there were any suggestions on what else it could be or any surefire way to tell if it really is the alternator.

I can't describe the noise too much better then a whirring, slight grinding type sound. The noise is the same at all times, no matter how long the car has been running or the temperature. It's a constant sound, at least to what I notice when I have it idling and am listening under the hood. I just really dont want whatever it is to seize if I'm out of town somewhere so I want to deal with the problem before it becomes a real problem. Thanks for all and any replies.

[Will Help]

You can do a fairly quick trouble shoot if you want to eliminate the engine itself. Remove the serpentine belt and start the engine. If no noise is heard then you can look elswhere. ( Do not run it too long. Might over heat. )

Both power steering pumps and a/c compressors can sound that way when they are ready to go.