Could be the idler or tensioner pulley bearing going bad. Don't wait much longer!
Each is bearing part number 6203-2RSJ (NAPA). Easy to replace just the bearing if your pulley is straight. There are various part numbers for those bearings (6203-xxxx) as they are used in lawn mowers, pulleys, etc, so you want to buy the better ones, which cost more and last longer (I hope).
If you PM me an e-mail address, I can send you photos of the pulley/bearing re-grease.
I dis-assemble and re-grease my pulley bearings and am using that 6203-2RSJ as a test for longevity. It cost 16.99 alone, which is about what a new pulley with a bearing costs.
If you are handy enough to do the underdrive pulley AND cheap, you too can re-grease them as a troubleshooting step for free. Again, I have photos for the asking.