Hard to tell from the phots but it looks to me like the front edge of each tread block is raised between the groove and sipe, by the ‘longitudinal’ sipe toward the inner edge. I’m not overly familiar with that tread pattern but that would tie in with what I’ve seen before on a number of sets of rear tyres, and would be enough to cause the noise. Not on my Cali but on a Passat. Mrs KB fixed the problem in the end by running into the vehicle in front and shortening the car by 12 inches or so
. Does it feel uneven when you run your hand over it? If so, may just be your issue.