There are several low-noise DC fans which are even quieter when run on less voltage, at the expense of less airflow.
I've experimented with an old CPU fan running off and 9v battery and it works. Don't know for how long, but it spins it fine and produces a very quiet airflow.
I've experimented with an old CPU fan running off and 9v battery and it works. Don't know for how long, but it spins it fine and produces a very quiet airflow.