We had a 1999 that had this issue from very early on. It was a bad idler assembly replaced under warranty.
Can you determine if it is the belt of the pulley? A bearing would normally be a low growl. Can you get a large screw driver safely onto the bearing or pulley bracket while it is running?
Also, do you have access to a stroboscope so that you can watch the belt while running?
I hate to use a belt dressing on a good belt, but you might try spraying a bit on the belt while running. Since the belt contacts on the flat side as well as the grooved side. there could be a bad spot in the belt on either side.
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