Hello! I have looked at very many threads regarding this topic, but couldn't find one that seems to be my exact situation so I am posting here, so I apologize if I missed a thread with my exact situation.
My Evo recently developed a quiet drivetrain whine which I am hoping isnt related to the transfer case, but doesn't seem to be. It is quiet enough that I would be lucky for the whine to be audible if I took a video. It increases in pitch the faster you go, and is loudest at 100km/h (highway speed). After that, it just gets drowned out by engine noise. It is also more noticeable on rough roads than on smooth roads. I have never launched the car, just the occasional roll racing.
With the front wheels in the air, I notice that when I turn one wheel, I can get ~ 10 degrees of rotation before it catches and makes the other wheel spin. I drained the transfer case fluid and rear diff fluid, and they showed no signs of wear whatsoever, and I am aware of the proper way to fill these transfer cases. When I drained the transmission, it had a bit more sludge on the drain plug, as well as a few metal shavings that were barely just big enough to be felt on my fingers. For fluids, I used AMSOIL 75w90MTL GL4 in the transmission, redline heavyweight shockproof GL5 in the transfer case, and redline 75w85 GL5 in the rear diff. Very difficult/expensive to get Diaqueen in Canada
That being said, I also installed polyurethane rear diff bushings about a month ago, and I've heard that they could potentially transmit a whining sound once they break in a little.

I would also like to note that my clutch is not good, and does rattle however the whine seems unrelated as I can make the clutch sounds go away by partially pressing it in enough to not disengage it while driving.

My question is do you guys think this noise is related to my transfer case, transmission, or just a byproduct of the new bushings?

Thanks everyone. Really hope its not transfer case related, as it seems it is no longer possible to get evo 4 - 6 transfer cases rebuilt due to parts no longer being available.

 

Anyone? Do these transmissions tend to whine when they are going out, or is it more likely tcase? Also I should mention that the whining usually happens on accel and decel, but sometimes only whines during acceleration, though somewhat rare. Its weird. It also still whines when car is coasting in neutral.

 

I had similar sound after changing my gearbox. In my case it was cover just above drive shaft. It was bend like 1 mm, impossible to see in first sight. These elements were so close to each other that when I accelerated or braked, they moved so close that they rubbed against each other and I heard a whistling sound. It was also whistling when I stopped the car but not always.