2008 Legacy 5 speed Trans whining

[mrtim4u]

Hey all,  I have a 2008 Legacy N/A Manual 5speed and something started whining. Ive replaced 3 wheel bearings now and when that didn't change it I did tires, That didnt change it..so I took it to a lift and the noise is coming from the bellhousing the tech said. It shifts smoothly, just continuously whines. It increase loudness/pitch with speed only. It doesn't change regardless of what gear it's in, clutch in, clutch out, neutral. I have rebuilt this 2.53 myself about 15k miles ago, also new clutch throw out new fork the whole nine. Never tore a manual trans apart before/yet so not sure whats inside that could be making this bad bearing sound, really loud 40-60mph

 

[MrEvanchi]

Had something similar, ended up being the center differential carrier bearings. Of course that'd be wheel speed dependent like yours. The whole tail-section of the transmission pops off which is where the countershaft, center differential, and all their bearings live. Not too difficult, it's just glued on with RTV which is tough to pop off. (There was a good writeup on the forum I referenced long ago when I did mine, including all part numbers.)
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Alternatively, those aren't the only bearings it could be. There's a solid chance your front differential bearings are the cause too, which would make much more sense if your mechanic very confidently narrowed it down the front, and not the rear of the transmission.
Mine manifested much like a whirring/whining noise, and only got worse and louder as I continued to drive it.