Brakes squeal 95% of the time after putting it in reverse.

My car is new.  It only has 5,600 miles on it.  Whenever it sits for a couple hours and I go to use it again, the brakes squeal when I put it in reverse.  I was told that after a car sits a little bit, brake dust builds up and that is the result.  I know that brake dust can do that but never heard of it on a new car like mine.  Also, I have never had that with any other car that I have had and I have had 4 brand new cars. This cannot be normal if it didn't even happen when my cars got hold.  What's up?