My sisters 07 had the same issue, was the glass separating from the top. Ford wouldn't cover it, costs over $1600 to have a new top put on.

 

157db is right IMHO. Must be a leak somewhere - it only makes sense.

I bought my 05 Vert last year and it had bad top then. Dealer knock $1000 off the price - he was going to put a top on but I figured he would put a "Piece O'Crap Top" on it so I took the discount and figured I'd put a better one on it. In the spring, I checked a few local places and the prices were $1200 to $1400, but I got lazy and didn't get it done. I think I may do it just before I put it away for the winter so the top can stay up to stretch out and set as I believe they like it to remain up for a period after the install.

Sorry for the partial hijack!

 

I did a test just for you.
I filled my fuel tank up
7/8 ths of the way full.
I did a bat turn into the parking space at
work and immediatly turned off the engine.
There was an enourmous amount of sloshing
like you are describing right behind me in the
rear seat bottoms area. Musta been gas because
I dont have a vert or water problems back there...

 

Hey Widowmaker. Discovered I have exactly the same issue on my 2013 mustang convertible. Did you ever get to the cause of the problem?