Here's the deal on mine.
~20,000 km (~12,000 miles) the brakes are vibrating at various speeds. Generally from 70-100 km/hr in a controlled stop.
Went to the dealer (I have a very good dealer - Valentine Volvo) and went for a spin with the shop manager - Bill.
He feels it, (he's a car guy) and thinks it's the rear brakes. In the shop, and the rear rotors (run-out) are way out of spec.
Rear spec is 0.075 mm, they are 0.184 mm. Rotors replaced.
Technician doesn't like the feel, back in the shop (did I mention that this is a good dealership?)
Checked the front run-out, and it's worse.
All four rotors replaced.
Brakes are good since.