Car in question: 97 Civic HX 5 speed, 226k.

About a month ago, the car started making a buzzing noise. It happens over 30 mph and goes away as soon as the car slows under 30 mph. It does it with the motor on and off, with the car in gear (tried all 5 plus being in neutral). Does it with the clutch in.

It DOES NOT make the noise with the front wheels in the air.
I thought maybe it was a wheel bearing. I replaced the front hub and bearings (both sides). It still made the noise, so I went ahead the replaced the rear hub and bearings. It still makes the noise. I can't find anything rubbing.

The transmission input shaft bearing and seal has been replaced as well as the clutch about 12k mi ago.

I need some suggestions! I am not sure where to go next and am not wanting to throw anymore money at the car and not produce results.

 

You sure it's not coming from the stereo? Could be noise coming through the stereo lines from the alternator

Dumb stuff to check:
Check for gravel pieces in tire tread
Check for metal scraps in grooves of tires

 

If it was the stereo/alternator, it should do it with the wheels off the ground right? I'll double check the tires.