Stability issues with postgres 6.5

I'm running postgres 6.5 on a basically bone stock Redhat 5.1 box.

On a separate machine, we have a PHP front end hitting the postgres
DB.  Everything works fine most of the time, but for no apparent
reason, every few weeks, the DB just dies.  ps shows plenty of
postgres process running, but telneting to port 5432 just returns
connection refused.  The error logs, as well as the postgres logs show
no information whatsoever.

Does anyone have any ideas what's going on?

Oren Teich