Droning noise
 

My 87 Carrera has developed a weird drone from the rear end. It occurs at around 78 MPH as a cyclical humming and increases to a steady hum at about 90MPH. It only occurs when I'm in 5th gear. Not present in 4th or when coasting in neutral and it's present as I accelerate and decelerate through those speed ranges.
Any thought would be greatly appreciated.
Chris

Check your trans fluid, make sure it full. Might want to check your rear wheel bearings too. Check the torque on your cv joints (both inner and outer on each axle).... Shift coupler adjusted correctly? No shifting problems? Wheel nuts torqued too?

I'm still chasing a trans noise/under car noise that started long time ago as a drone. Doing rear bearings among other wear items looking for the issue...