2 Brand new Foresters 2010. When in reverse and then going forward after about 20 ft there is this noise that comes from the back rear,passenger side. It sounds like a locking noise. Like when you lock the doors. We've got out and checked the trunk even to see if that was it. My hub says it only happens on his car when it is cold. Two new cars with this same sound. Dealer said to bring in in the morning, would like to have some info prior. Also, subaru mechanic was asked and really did not know. Any suggestions? Thanks, Happy Easter.