OK, first thing. In a car, always refer to right or left as though you are sitting in the driver's seat ready to drive the car. Any other way is confusing. Alternately you can pretend that you are standing on your head on the hood facing the windshield. Picture that if you can. Right and left would still be the same as if you were a driver.
I would guess that you are starting to lose an idler pulley bearing or the bearing on the belt tensioner.
