STRANGE Drive Train Noise – Infiniti G20 – 1999

1999 Infiniti G20. 145,000 miles. Auto trans. This problem just started recently. As you accelerate a humming noise increases in pitch throughout acceleration. It sounds like when you pass a large 4WD truck with monster tread tires…that whirring, humming sound. It does not happen while in neutral while stationary and revving the engine, so I know it’s not an engine bearing – only while on the road while moving. It does happen while coasting in neutral at speed. The trans also shifts perfectly so I don’t think it’s involved and the tire pressure is correct ,so I put it up on blocks and got underneath. It appears to be coming from down near the transmission/differential or axles. But this car had both axles replaced less than a year ago. Originally, I thought it might be the wheel bearings. But when I lifted the car and wiggled the wheels, I found no play and the noise seemed to be coming from farther in than at the area where the wheel bearings would be. It was there even while spinning the wheels freely by hand while on the lift. I think this car has a differential bearing and wonder about that or maybe it’s the wheel bearings and I just didn’t hear the location correctly. Or maybe the axles were done wrong…? Can anybody help me identify this problem? Thanks! – JL