  In this Letter we study the gravitational interactions between outgoing
configurations giving rise to Hawking radiation and in-falling configurations.
When the latter are in their ground state, the near horizon interactions lead
to collective effects which express themselves as metric fluctuations and which
induce dissipation, as in Brownian motion. This dissipation prevents the
appearance of trans-Planckian frequencies and leads to a description of Hawking
radiation which is very similar to that obtained from sound propagation in
condensed matter models.
