Originally Posted by Pal215

All it takes is for someone to buy an evo who is unfamiliar with how it is supposed to sound and then go online and read one of those posts that say something like "Evos are noisy cars and just make all kinds of noises naturally" to just completely ignore the problem and obliterate the drivetrain.

I have this crazy theory that the quieter your drivetrain is, the more correctly meshed and correctly broken in your gears are. Even crazier? I believe that any oem style transmission, diff, or TC part should sound only as loud as when the car was built new. If it sounds any different than that, i'd be concerned. Clutches are neither here nor there.

Originally Posted by kaj

With no interior and poly mounts, my rear diff was pretty whiney. I was told that's not normal. I got it back from TRE and it's exactly the same. so I assume it made the same noise from the factory.

Originally Posted by 2006EvoIXer

Do you have "upgraded" rear diff bushings? My rear diff whined like a pig getting slaughtered between 60-80mph (80 at loudest). It showed up when I changed those bushings to get rid of my thumps every time i let off throttle. I read that it was rear diff going bad, but recently confirmed that it was these bushings (thanks to @Lumpy Sticks ). Cant believe everything you read, no matter who it is. Lol.
Anyway, it is the bolt rubbing on metal washer causing rear diff whine. I probably had the whine for less than 3,000 miles to groove the washers: