Rust??!! Nothing like a well looked after Zed and that sounds like it was nothing like a well looked after Zed! I hope it works out for you, buddy. I love my Zed and think i'm obsessed!!
My guess would be under the paint. Mine is doing this now. As per quite a lot of the Nissan paint, its not the best! Carbon bonnet for me soon when I cant stand it any more! There was no sign of it when I bought the car 2yrs ago, its been caused by stone chips in the last 2yrs