fixitmr is correct, but could also be a first sign of either the Idler or Tensioner Pulley Bearing going bad.
Try this - with engine off and spray lube in hand, locate the idler and tensioner pulleys (it may only have a tensioner). Spray around the center bolt, start engine and rev or take for test drive and excelerate hard. If no noise then would replace pulley. If still present turn engine off and spray center bolt of idler if has one and repeat test above. If noise gone replace pulley. If still present spray belt and repeat test above. If noise gone replace belt.