When I started up my car (1972 1.7 /4) this morn after it had been sitting for almost a month, I heard a loud squeaking from the engine compartment that sounds like a loose belt. I assume this is the fan belt since I can't think of any other belts (no water pump, no A/C, etc.) I can still hear the fan running. How serious is this, and how hard will it be to replace?