Michelin Pilot Primacy tyres on 530d

[steve-V8s]

The original rubber on my 530d was Pilot Primacy 235/45/17. Towards the end of the life of the first set the fronts became very noisy at low speed. These were replaced with a set of Pilot Sport which ran right to the end without the noise symptom, they were then replaced with another set of Pilot Primacy. The fronts have now done around 18k miles and have a lot of wear left but are generating noise and vibration at low speeds. Looking at the tyre it has two distinct tread patterns, the outer part being a radial pattern and the inner part consisting of blocks. I think that the noise comes from these blocks which have not all worn to the same level. Running a hand over them reveals that some blocks are noticeably more worn than others. The suspension geometry checks out OK and the pressures are kept as per the handbook. Has anybody else noticed this problem ?