I drive an evo 4 gsr (ayc diff) there is a whining noise from rear. Gets louder at higher speeds but not louder with more acceleration. Havnt owned the car for long. Im sure its not the diff any other suggestions of what to check or what could be wrong?

 

Have a quick read through each of these threads:
https://www.evolutionm.net/forums/ev...ne-normal.html
https://www.evolutionm.net/forums/ev...ing-whine.html
https://www.evolutionm.net/forums/ev...nows-what.html
https://www.evolutionm.net/forums/ev...ming-rear.html

I have a bit of a noise coming from the rear (mechanical non AYC diff). It gets louder with speed and is loudest at 50-60kmh (not sure if road noise starts to drown it out after that or not). It's definitely louder when colder. I drove up the Coromandel Peninsula (from Hamilton) yesterday and I couldn't hear it at all at any speed when I got back.

I've changed the fluids in the diff, no effect. I'm getting around to inspecting the rear wheel bearings. And if that's not it then I'll look at the pads and rotors on the rear.