I bought the black energy suspension rear differential bushings and only changed the mount bushings and not the mustache bar ones (seems like a pain to do). Anyways the famous clunk is gone but now I got a noticeable whine which I can hear in most gears. It's quieter in 5th gear and louder in higher gears. What could it be?

 

Differential noise. A new ring and pinion gear with proper setup will make it go away.

 

Mine does the same thing. I took it to a local shop and they said it checks out fine.
I removed my interior at the same time, so that probably makes it seem even worse. Lol

 

It's "normal" in the sense that gear setup from factory sucks in these cars. Whining went away for me with a gear set and correct setup of the contact pattern.

 

I would send it in to be serviced and have the plates restacked correctly.
http://www.teamrip.com/EVOLUTION%20R...20SERVICE.html
http://sheptrans.com/product/evo-4-9...ntial-service/

 

I don't mind. My Mustang did the same thing. I don't even notice it any more.

 

So technically nothing is wrong? I did hear a tiny whine just before I changed the bushings, but it wasn't anything that really distracted me, but it got noticeably louder as soon as I changed the bushings. Also changed the fluid with OEM diaqueen. Will the diff eventually fail on me or is it a normal whine? Also, my trunk had no carpets so that might be increasing the sound a little bit

 

stiffer bushings = less vibration dampening. You will definitely hear more. My car sounds like I have straight-cut gears, since the inside is basically a drum now LOL.
FWIW I have 130k miles on my rear differential. I swapped bushings out two years ago. If it dies, it dies and I'll have it rebuilt.

 

The reason the factory bushings are soft and clunk is to isolate gear noise.

 

Nothing is particularly "wrong". It will go a long ways making some noise. But the noise can be dealt with by replacing the gear set.

 

Yeah changing the bushings usually results in louder cabin noise and whine, this is completely normal on our cars.