On my 2000 OBW, I have recently started getting a slight vibration in the steering wheel when I'm travelling within a certain speed range, like between 90 kph (55mph) and 110 kph (70 mph). Above or below that, and the vibration disappears.
I checked the tire pressures, and found that there was a 5 psi difference between the two front tires, so I pumped them up as close as possible. That seems to have reduced the vibration even more, but it's still slightly there.
I had an old Volkswagen years ago, which exhibited these traits at one time, and I found out that it was steering joint that was deteriorating and certain speed caused a harmonic in that arm causing the vibration. I hope I'm not seeing the same thing here with the Outback.
Yousuf Khan