Technical Strange Hum underneath Maybe a fuel pump??

[jiminnella]

My 1983 Spider runs great. Took it to a cars & coffee yesterday and it drove great. It was cold so I had the top up (which I really do). Took it for a drive this morning and heard a hum from the rear and underneath. The hum increases and decreases in sound as I accelerate and decelerate. I have the same hum with the car standing still. I changed out the fuel pump and filter within 500 miles ago. I'm guessing it has to do with fuel and I believe the noise is near the area of the fuel pump. The car is not starving for fuel and accelerates as good as ever. Any thoughts?? Could it have always made that hum and I never heard it with the top down??
Thanks for any suggestions