2011 Armada has a rattling bumping sound coming from the back end

I just got this Nissan last week. I am going to take it in to the dealer this week and have it checked out but I was wondering if anyone else had this happen to them. It would help me to know what I am talking about when I talk to the "professionals". The rear end is making a bumping/rattling sound when I slow down and when I go over an uneven surface. You can actually feel the bumping through the car as well as hear it. It just started doing it yesterday and like I said I have only had it a week.  I traded in my 2004 Armada for this one and was loving how quiet it was. My 2004 Armada rattled and squeaked all over the place. I don't want to have that happen again. Thanks for your input.