They might simply have been bad tyres from new but it took a couple of years for this to become apparent. Could also have suffered carcass damage on a pothole. Far more likely with 17-inch or 18-inch wheels than with 15-inch or 16-inch, in which case the rims may also be damaged. Bit difficult to argue as a warranty issue. Get the tyres fitted and balanced first. If the fitter reports that the wheels are out of true then you may need new wheels. If not, try the car on the new tyres. If you still have a problem, get the alignment checked at a branch of www.alignmycar.co.uk/ I recommend Michelin Cross Climate or Goodyear Vector 4 Seasons Gen 2 tyres all round if you're prepared to buy four. But must be a full set.