2012 V60 T6 Vibration deceleration

[v60t6kiwi]

Hi everyone, I've been searching and searching for a fix for this but have not come across any.

During deceleration through about 50kph, a vibration starts and gets progressively worse until 40kph where it is the most noticeable.
As soon as I use the brake, it disappears. But when I release the brake it comes back. I'm 80% sure it's coming from the rear.

I have tried:
Wheel balance and alignment (which I thought fixed it but it's back)
New rear rotors and pads.

I've had it at the dealer for a usual service and they couldn't find anything blatantly obvious (I didn't tell them to diagnose fully)

Any help or thoughts are appreciated.