Without knowing how hot the gear box is you are shooting in the dark. Your hot water heater is probably set around 120 degrees, hot enough you do not want to hold your hands under it, but 120 degrees for a gearbox is a cool running gearbox. Generally a gearbox will run about 50 degrees hotter than the ambient temperature. Add that to the heat generated by a belt drive and the temperature will be higher.
Now, since you think it sounds differently, then you should investigate closer before any damage is done. The top bearing on those gearboxes is what usually fails causing internal damage from the debris falling into the gearbox. Loosening the belt will allow you to see if there is any play in the bearing.