Could there be two distinct concepts being confused here?

1. A graviton could give rise to another (albeit lesser) graviton, thus increasing the total gravitational energy.

2. A graviton might convert into a number of lesser gravitons, thus increasing the number of gravitons, but not the total gravitational energy.

If 1 is the case, how could this contribute to run-away gravity?

If 2 is the case; where does the additional energy come from?

There never was nothing.