Grinding noises coming from the rear of your BMW M4

HI

I have booked my car at BMW Zambezi , its been two days now while waiting for my car to be repaired but the way things are going i am not happy ,my frustration is that i was told ,the dealer is waiting for car similar to mine to come in and the will swap Tyre's to test reason being that my back wheel Tyre's thread are not the same the other option i was given is to buy two new Tyre's so they can continue withe test or i have to wait , if noise has been proven that its not on the Tyre's they will look towards on replacing the wheel bearing , why should i buy two new Tyre's for BMW to do diagnostics

I have once reported the similar noise to ABM BMW i was told it could be a stone stuck on the brakes , i have provided a link similar to my noise below .

https://www.youtube.com/watch?v=0auQ0l-OGSQ

Can someone at BMW answer me if BMW don't have the solution to this noise