I've been following this thread for about the last few months quietly (first post!) and I must say, there's a lot of weird information floating around out there. Let's back it up and just clarify a few things to help out the TLDR crowd.
Vibration -
There's a persistent vibration coming from the rear axle of the car and its not vehicle-speed dependent (harmonic).
- It's NOT a tire imbalance issue
- It's NOT related to the car being a "body on frame" design
- It's NOT related to how the car is sprung (this isn't a 2500 series RAM, it's a Lexus)
- It's NOT related to it being "designed for off-road use" (it's designed for street use with some extra rigor for the off-road stuff)
- Though I can tell you it's not any of the above, I'm short of being able to identify what it actually is!
Brakes-
I don't think it's got anything to do with the brakes as a sticky caliper would prevent it from tracking straight which does not appear to be an issue (I know this because Porsche Torque Vectoring uses the brakes on the inside rear wheel to help the car rotate in). To me, something is impacting one/both of the rear shocks.