[Hal Adams]

So, is your trunk lid closing properly? Did you have to force it shut? Did you just lift the seperator before this happened?
It could be that it is the seperator is not closed properly.

 

[Hal Adams]

some rain has made its way into the trunk...it is not sopping wet, just a bit damp.

Are you still under warranty? There is a weak spot in the trunk sealing rubbers, especially the top one.
Mine was the same and just had it done. It is now perfect.