1996 Ford Ranger Squealing noise when gas pedal depressed

Good afternoon gentlemen! I have a 1996 Ford Ranger with the original clutch and 150K miles. I have been very careful about paying close attention to this vehicle and have kept it regularly maintenanced with oil changes, air and fuel filter changes, and general upkeep. It has a new alternator, starter, spark plugs and wires, and battery. The check engine light has been on for about a year and my mechanic plugged it into his machine and said that my 02 sensor is out. He said that wasn't a huge deal and was not something that needed to be fixed immediately. When driving, when the gas pedal is depressed, it just started making a strange squealing noise. Can you please comment? The gas gauge has not worked for years. Thanks and I will make a donation on future requests if your advice pans out!