Blender is eating GB's of HD space when rendering Blender is eating GB's of HD space when rendering.
Its uses up around 5GB for a few hundred frames of animation and doesn't release it after its finished.
I gather this may have been because I had cache BVH ticked.

I'm on osx 10.9 but can't for the life of me find any BVH files?
How do i find them on a Mac, or is my problem elsewhere?
The bvh cache files can be found in a folder called cache that will be located in the same folder as the config folder that contains startup.blend, the filenames start with bvh_ followed by a unique 32 character string. 

See this page for details about where the config folder can be found.

This question has more info on when the BVH Cache can be helpful.