I searched around a bit but mostly found info about whine noise in 1st - 3rd. In my Car 84 firebird with a 355 NWC t5 transmission and 3.73 L69 rear gears with locking kit installed. I have topped off all fluids. If I am traveling between 42-48mps in 4th or 5th I can hear a whining noise coming somewhere from next to or behind me hard to tell. It goes away a lot when I let off the gas and becomes intermittent as the car rocks back and forth and seems to go away I push harder on the gas. The noise seems to be the loudest when I am just maintaining speed. Any ideas?

 

Bump with update it seems to be quieter on hot days not when the car warms out but on hot days. Also I can hear it at higher speeds but it is higher pitched and quieter but still only in 4th and 5th gear.