Recently bought a 2021 edition 1 q5. When on full lock there's an awful grinding, grating noise. It has 255x40x21 tyres/wheels. To me it feels like the tyres are scrubbing side ways when turning, or maybe even the diff is grating. Initially Audi said it was probably  because of the low profile tyres! 

Anybody come across this before

Hello Kevin,

I’ve removed your duplicate post for you. 
Re. the issue:- 

Have you checked that 245/40/21 is a correct and listed alternative fitment for your vehicle? 
The answer will be on the tyre pressure sticker on the car - fuel flap, door pillar etc. 

Is the car fitted with mud flaps? 
Kind regards,

Gareth.