The sound starts around 20 mph. Driving the car and hearing the echo off stuff to the side of the car it sounds like a backing plate hitting a rotor. The front rotors are not hitting the plates and the rears don't make any sounds. This isn't that reliable since you have the sound of rushing air. You can't get slow enough to identify the sound. Well I put it up on stands today and spun the wheels with the engine. The recorded sound goes up around 40 mph. It should be good enough quality. The sound is definitely coming from the rear axle somewhere in the middle. U-joints are brand new. I pried the slinger a few hairs away from the differential, no change in the sound there. It does make a sound when I turn the shaft by hand. I am close to getting a newer rear, anyway, to use the newer discs instead of these weird ones with the e-brake problem and being on opposite sides. Also because my posi doesn't seem to work. What's it sound like?

http://timramich.com/fbody/mystery-noise.m4a

It's not the slinger I moved. It's the shield attached to the flange assembly.

 

No one has any idea what it is? The sound starts around the 10-11 second area.