The rear end noise is from the clutches chattering. GM has the wrong fluid in them. Dealer will flush it out and add correct fluid and the problem will be fixed. If your power steering is making noise GM is working on a part to fix it, ask your dealer to notify you when it is available.

 

my car has 5,000 miles & was making a lot of noise at low rates of speed while turning in parking lots, took it to dealer who immediately knew what the problem was, said there was a "service bulletin" issued regarding this issue & they had actually had several in for the same thing, they changed out the fluid about 2 weeks ago & I haven't heard the grinding since.