Water Coming In My 2008 Mustang.

I have a 2008 convertible mustang that has water coming in. I notice every time I pull out of the driveway after it rains the sound of water moving around but did not see any leaks. Last week I notice water at the back side of my convertible. It is behind the seats right by the back window. I assume this is the water noise I am hearing.

I have read that there are two water drains for the Mustang models. One in the front under the hood and one along the side of the car. I will search for the second one and see where the water is coming from. Does anyone have any clue about this?