It's basically a loud helicopter-like noise, kind of like when you have two windows open. Varies with wheel speed, doesn't matter if it's in gear or neutral. Definitely coming from the rear axle, not sure if left, right or center.

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id say wheel bearing, try to take tight corners and see if it gets stronger on one side or another, also, another simple check, jack the car up on each wheel one by one, take off the wheel, and spin the rotor, if one is making a more noticable dragging noise, you've found your problem.

 

^this my money is on bearing least
you should hope it's the bearing haha but ya. youl notice the difference when you get the car jacked up spin the wheels and listen for any louder sound. usually when one bearing goes the other goes soon after so I'd replace both. diff would be more like whine sound higher pitch. I've been through every possible evo problem dear god..lol

 

.lol! sorry to hear that bro, its sad to hear a fellow evo owner having problems with their car. but yes like you said, diff would have a much higher pitch due to the ring gear spinning much faster than your wheels would. Or atleast that what I think would happen. It's quite possibly your wheel bearing.

 

+1 on the wheel bearing.
Try taking off the wheels and spinning each side by the rotor to see if any noise or resistance will come. Hopefully you find the problem.