We have a 2011 Outback 2.5 with 165k miles and CVT. Over the last 6 months, an enigmatic vibration has developed in the driveline somewhere that – for lack of a better description – makes it feel like we’re running on muddy terrain tires. I’m running out of troubleshooting ideas and would really appreciate some input from the Subaru gurus of the world! The bullet points of capture are below…
Symptoms:
– Vibration frequency is low-medium, i.e. higher than the RPM of the spinning wheels, but lower than the rotating components of the engine. My best estimate is in the 20-100 hZ range, completely speed dependent.
– Frequency only increases linearly with vehicle speed, first noticeable around 25 mph (ie not engine RPM).
– Disengaging the transmission in neutral while driving makes no difference, nor does the selected CVT “gear ratio”.
What have I done:
– Tires are 5 months old with 5k miles now (Goodyear Assurance All Season) and were shop balanced (although vibration frequency does not suggest tire imbalance).
– Complete lineup of recent times.
– Replaced the rear axle shaft assembly, making a slight improvement due to a deteriorating U-link and aging center carrier (main problem still persists).
-Frequently changed front and rear diff oils with no evidence of magneto or fluid issues.
– The wheels spin freely while in the lift, and the bearings seem to pass the usual tests.
– With all four wheels off the ground, the problem is almost identical when accelerating up to 50 mph (suggests that the problem is not related to the wheels or tires)
I have not been able to pinpoint the exact location of this vibration, as it is slightly felt through the steering wheel, although it can be heard throughout the interior of the car as if coming from any angle. I’m 99% sure I’ve ruled out the engine, CVT, wheels/tires, or rear axle, although I’m on the fence about axle shafts and CV joints…and I hate throwing parts into the fray to see what works. 
Thanks everyone for every contribution!
-Jeff in Lynn, MA
