Steering has slight wobble at 30 mph

[Flatheadron]

Our 2012 Outback has developed a very slight wobble in the steering wheel at 30 MPH. I might describe it as a nibble. you only feel it is the wheel, no sensation in the seat. It is similar to what you would feel if you had a tire ply separation but nowhere near that extreme. Happens at a small range of speeds around 30-35 MPH. Gone above and below that. Tires are new within the last year; front end was checked out by our mechanic and found no problems. All steering joints have no play. Ran tire lateral and radial runouts on both front tires, all runout readings were in the range of .030"-.040", which is in spec. Any ideas?