1992 Camaro Z28 - For the passed year I've had a symptom where my fuel tank pressure control valve just beside the rear driver wheel (little plastic valve) HUMS LOUDLY.. Seems to occur more when the tank is 1/2 up to almost empty.

It will HUM loudly for around 5 seconds, and then disappear.. Then do it again.. and off. We know it's this valve as the car was on the hoist before and we can put our hand over the plastic valve and it will muffle the sound.

Is this serious? since it's releasing the pressure in the tank does this mean it's NOT releasing properly? Can a explosion occur if not fixed? Does all it mean is to just replace that valve?

Thanks