I had the same annoying rattle shortly after buying my 2017 Cascada. I ended up sitting in the back while my wife drove me around until I found the noise. With the Top halfway up you can see a 2 prong fork bracket. Those prongs end up around a little roller once the top is up. I started out with a spray lubricant (WD-40) on the roller which completely eliminated the noise. A simple spray seams to last a couple of months then needs to be reapplied. I got tired of that and applied a paste style lubricant to the roller and have not had any noise since (about 4 months now).