GRD-4-3L to the HVAC (heating/ventilation/AC) rescue!
Case 1: Your blower wheel is cracked/damaged and rubbing against blower housing. Remove blower motor/wheel assembly, then visually inspect the outer shell of the blower wheel. If you see rubbing marks on it, you know it is the blower wheel. Cheap & easy to replace.
Case 2: You have leaf or other obstruction that is rubbing against the blower wheel. Sort of like sticking a card in rotating bicycle wheel. Remove obstruction from the blower wheel and off you go. Might as well clean up the HVAC inlet duct while you are at it. Chances are, you have more debris waiting to fall into the blower.
Case 3: You have cricket in you dash. Release a large rat or a reptile in your car overnight. Remove the large rat or reptile in the morning. Don't forget to remove tiny black pellets.