Free memory from arrays

I am making a game. Whenever a level is created, a few large arrays are filled up with numbers. The memory usage is around 3mb.

When I want to load a new level, I want to remove these arrays from memory and repopulate them with the data from a new level. But, no matter what I do, the game keeps on using up an extra ~3mb of memory each time I reload a level.

The arrays are not being removed from memory.

I have tried setting every element of every array to null, I have tried setting the arrays themselves to null, I have tried using myarray.splice(0) to remove the elements from the array, but the memory is still not being freed.

Why would this be happening? The memory usage is not from movieclips, it is just arrays with numbers in them. And it seems to me like it is impossible to delete them.

Why would this be happening? How do I force flash to remove the arrays from memory?

Thanks