I recently purchased a 2-year old Audi A5 Cabriolet S-Line 2.0 diesel front wheel drive, which is fitted with 18-inch rims, Continental Sport Contact 3 tyres on the front and Avon ZZ5 tyres on the rear. The size of tyre is 245/40 R18 and all four are about 40 per cent worn. I inspected the tyres and there do not appear to be any defects or uneven wear. At motorway speeds I am experiencing an unpleasant droning noise that seems to come from the rear. At lower speeds there is just the usual roar from rough surfaces. Firstly, are the Avon tyres suitable for this model or are they known to be noisy? Would the replacement of the Avons with Continental Sport Contact 3 on the rear eliminate or reduce this droning noise? Would changing the wheels to 17-inch with Continental tyres reduce the noise and improve the driving experience? Apart from the noise, the car is superb.