1954 chevy bel-air

I have a 54 chevy bel-air with a 2-speed powerglide. everything works fine. recently after just sitting for a month the car started making a weird humming/whining noise when it hits 60mph. if i step on the accelerator and drive up to 70 mph the noicfe goes away. any ideas?

Welcome to AF, I am working on the same car in my shop as we speak. Many things can cause this, bad wheel/axle bearing, uneven worn tire, noisey rear diff. No way to tell without a road test. Run the car rear wheels off the ground, be careful of course, see if you hear any nosise, I would not recommnend 60 on the jacks though.