Had to replace 4 Left front tires due to defect.

I bought the car just over 2 years old with 16500 miles on it. Originally at 23000 miles the L.F tire started to give "Whop Whop sound" I replaced it with a new one and at the same time rotated them. ie. put new tire on R. side.Rear tires are different size to front, so switched left to right. At 34000 miles again that L.H.tire did the same. That was an original tire and was replaced with new. Both of those new tires eventually produced the same sound. (They are Michelin's and they, Michelin, gave me 35% off each new tires I replaced tires 3 and 4 with.---Good will) One answer I was given to this problem could be due to the strut dampers. I tend to accept that explanation over that of the rotors as my dealership in early days did put good wheels on from another car which felt better. My understanding is that a faulty damper operation generates the fault over time. One other point is I feel NO Lateral runout from the rotors when braking.