Mazda 2 grinding noice

I bought a brand new mazda 2
I bought it under the toyota yaris label
As soon as bought it was making loud grinding sounds from the rear end
I took it the dealer and he said he checked the brakes and couldn t find I told obviously it has nothing to do with the brakes . Then he said he has never heard of this problem before.
I guess he has never seen this forum obviously it is a common problem with the mazda 2