Knocking/creaking noise from rear

I have recently noticed a dull knocking/creaking noise that sounds like it is coming from the area around the back of the rear right door. It only happens at low speed. I have now discovered that it tends to happen most when I reverse around a slight bend with adverse camber on the road, i.e. when the chassis flexes. 

Car is a 2016 VRS 4x4. 

An ideas what what this noise could be? Thanks