Sounds like you have water in the bottom of the trunk. It is a common problem and can get expensive if not dealt with. You can use the search box in the upper right corner of the forum to find a lot of information, or click this link to get a good start. water in trunk
Glad you have help with this. You can try to slide a piece of paper between the foam (under the carpet) at the front edge in the trunk to get into the well that sits under the foam. The air pump which opens and closes your locks is in there and it is connected to the anti theft system. Also look on the drivers side under the foam. On the drivers side there is actually an open square in the foam under the repair kit that you can very easily slide a piece of paper forward to check for water, but it is the passenger side that has the pump and more than likely is where your problem has occurred.