general problems of the 2004 Mercedes Benz ML500

I have returned my SUV to mercedes about 5 times to have the brakes replaced because they squeal when stopping. I have been told my mercedes that there is nothing that can be done because all disc brakes squeal. I find this hard to believe because I have had many cars with disc brakes over the years. I picked the car up on 2/3/05 and it was squealing again on 2/4/05.