Are you sure it's coming from where you think? I had a similar rattle and kept checking under the dash. Eventually I realized it was coming from underneath the console. I opened up the emergency disconnect door in the back row, started to feel around inside and found that one of the tabs holding some cables had come undone and the cables were flopping around. I ended up getting some thick tape and taping the cable to the interior side and the rattle is gone.
My 2013 Leaf also rattles from the dash. I am not sure if it's coming from the speedo are, the radio bezel or the front dash close to the windshield. I only hear it when the radio and A/C if off and driving at slow speeds.
Hey guys, I think I may have found the source in my 2013 Leaf of the Dashboard/windscreen rattle after it has been driving me nuts for a year:
The problem is that the metal of the top of the firewall where it folds over forward and glues to the lower edge of the windscreen is thin, flexible and resonates on rough road surfaces. In particular the little downwards point tab that has the VIN number on it vibrates like a tuning fork in an ash tray full of washers. (There is a plastic inspection hatch beneath the wiper arms in the center of the lower windscreen shroud that can be removed in order to seen the offending tab and read the VIN).
By putting big globs of silicon sealant on the back of it (I'm talking about a cup full), it has helped a lot to reduce the noise. I guess it will work if you put it on the front face but it will obscure the VIN number.
To get good access I had to remove the plastic covers and wind screen wiper arms. Don't forget to clean the dust and grime off of it so that the silicon has a good surface to adhere to. I'm also planning to put that thick black tar like under-body sealer on the firewall behind this tab to further help with the noise.