I had a similer problem with 'Stepped' Tyres, on a Peugeot'though that wasnt the term the guy used. It is due to uneven wear caused by a slight misalignment of the suspension. this is usually due to worn bushes and other things. It reduces Tyre life, but not usually by enough to pay for the replacement bushes etc. You can feel it if you run your Hand gently over the surface of the Tyre (sideways across the tread)It will feel smooth one way but slightly rough the other.
On the subject of noisy Tyres, my 156 had Michelin 205 / 55 fitted from new, as they wore they became so noisy I thought a wheel bearing had gone. I had it booked in for the Bearings replacing when after swapping the Tyres to Pirellis the noise wentaway. Mind you the kind dealer swapped a bearing anyway!!. The Pirellis are half worn now with no real noise so far.