09 Impreza Outback Sport, rear-end shimmy ~40mph

[09Imprez]

I've recently started having an issue with the right-rear of the car starting to shimmy around 40mph.  Sometimes it will start earlier, but that's the consistent mph.  The shimmy will persist while decelerating, braking, and even in neutral (I have a 5-speed manual transmission) until I have come to a full stop.  It's not a tire balance issue as it persists even after swapping front/rear tires.  I've replaced the rotors and pads and cleaned up the e-brakes since it started so that should eliminate those factors.  Wheels and tires are all four the same.  First time posting on a forum so not sure what other information would be useful but any help is appreciated on what the cause may be or further troubleshooting to do.  Thanks!

[forester2002s]

Is there an audible component to the 'shimmy'?  Like a 'rumbling' sound?

If so, one of the wheel-bearings could be on the way out.

[1 Lucky Texan]

you didn't specifically mention but, the calipers are free to slide on their pins?

[heartless]

check suspension components carefully... you have ruled out the immediate obvious stuff.

bad strut, worn bushings, wheel bearing, possibly even an axle problem could all contribute to a shimmy

quick & dirty test for a wheel bearing, check the hub temp after driving for a bit.. frequently a bad bearing will cause the hub to be significantly warmer than the rest

[09Imprez]

@Forester, there is a low rumbling to make me think it's the bearings.

@1lucky, the calipers are free on their pins.

@heartless, I'll double check the suspension and never thought to check temp do will do that. 

For the most part I'm thinking hub replacement is the way to go. Thanks!

[Rampage]

54 minutes ago, 09Imprez said:

For the most part I'm thinking hub replacement is the way to go.

Good idea replacing the hub and bearing as an assembly.

I have pulled the inner races of the bearing off the hub and see grooves worn in the hub from the inner races.