Apparently a loose battery tie-down...
 

...sounds like someone dumped a bunch of nickels in the trunk. Spent 5 minutes searching for the source of the rattle, even shook the battery once but didn't notice it was loose till the second time I grabbed it.

:loser:

In other news, if the temperature has dropped significantly where you are, it's worth checking and adjusting your hardtop/softtop latches. Mine were all a little looser than I usually run them.

Good to know if anyone else has the same noises!

QFT

At the back end of the first good cold front last fall I engage in some shameful shamful street racing with a new yellow Camaro. I'm pretty sure he had a V8 because he was pulling away from me.

At 90mph it ceased to matter when the soft top flipped open. I swear I had tightened the latches a month earlier.

The previous owner of my miata just bought a large sized battery, threw it in the back without tie downs, and now the rear quarter panel has two battery sized dents on the outside. That and battery acid leaked everywhere (seemingly when the battery split apart), so I'm always dealing with surface rust issues. I hate people.