LOUD whine in reverse

[kookookachew]

Well, the other day the Subaru was parked in the yard and I went to back it up. I did so in a... quick manner; resulting in what felt like axle-hop from the rear end, it was not pleasant. Then I immediately noticed a very distinctly wrong whining noise from either the transmission or front differential. Its much louder than the typical manual transmission reverse whine, and is most noticeable when decelerating in reverse. I've attached a video of the noise, any information on what it could be, and how serious would be great.

Thanks guys!

http://www.youtube.com/watch?v=HKf79oKCqVo

[ouch1011]

Well thats definitely the reverse gear set whining. Does it make noise in any other gears? I've not torn apart a Subaru trans, so I don't know exactly where the reverse gear set is located in the trans, but the fact that it only happens on decel leads me to believe that there may be a problem with how the gear teeth are contacting each other only on decel.

[kookookachew]

Thankfully, all other gears sound fine. Still shifts fine, and moves fine, you wouldnt know anything is wrong except for that noise.