I have a 2002 Outback I bought in '06 with about 75k miles. It now has 222k miles and the engine still runs strong (no head gasket problems yet, at least no oil and coolant mixing). I recently purchased a used transmission from a website willing to warranty it. Subsequent to its installation I drove away from the shop happy it was over. Apparently, the mechanic did not test drive it at highway speeds, only on in town roads. When I first got to about 70 mph a terrible noise and "shudder" started and would not stop until I came to a complete stop. There was some kind of resistance like almost like the rotor was warped, but this possibility was fairly quickly eliminated. It really felt like the whole car was going to fly apart. We determined the problem was the U-joints in the prop shaft (even from a second opinion, damned non-serviceable u-joints!). I obtained a new prop shaft (couldn't get a used one quickly enough and for a price that justified going used) and had it installed. The same thing still occurred, only it took longer now to show up. I didn't go straight back to the mechanic's because it was closing time. I drove the car more that evening at lower speeds where the problem doesn't rear its head, however; when I made a pit stop and parked on a hill the problem "changed". The hill was enough of a grade that I didn't put the car into reverse to back out of my parking space, I just pushed the clutch in to coast backward. The car moved maybe 3 feet and stopped like it was in a forward gear; I put it into reverse expecting to hear some terrible clunk like I was ripping some part of tranny out in doing so, but nothing...the car seemed to move on to the next moment as if nothing out of the ordinary occurred. As I drove a little more this was not the case either. I began to hear a noise, I believe from the tranny, similar to what you might hear if you ever put a playing card in the spokes of your bicycle as a kid. It's a cross between that and the sound a bad heater blower fan might make. This new noise happens in gears 2 - 5 and occurs when accelerating (what I call positive torque) and when I make the engine turn just fast enough to match the spin of the transmission resulting from the velocity I am travelling (what I would call neutral torque). It does not happen in a "negative torque" condition (the force of decelerating by simply leaving the car in gear and letting off the accelerator, producing torque in the opposite direction of that for accelerating). My old tranny made a similar noise in the negative torque condition for a long time, and I think was the ultimate cause for the need of a new one. In dealing with the transmission seller, we have gone through a litany of possible problems, each eliminated one by one. Their last (or at least most recent) suggestion is that the carrier bearing might be bad. Any thoughts or additional suggestions? I think it is still something in the tranny (no idea what internal part) or maaaayybe some issue with the aftermarket clutch installed at the same time. Oh, one additional note, the high speed shudder went away when the new noise showed up. Now only a slight shimmy between 68 & 73 mph; feels more like a bad motor mount now but I know that won't cause the new noise. I don't think the original shudder and noise is motor mount related either because I think it would go away if I slow down. Additionally I think it would happen in a certain rpm range if it was motor mount related...not at a certain speed.
Sorry for the long narrative, but I think it in needed since responders can't test drive it.