Rails 3.2 Periodic errors in nginx error log

Hi,

I have a simple Rails 3.2 application that seems to be working fine, but every 20 minutes, a set of errors like this shows up in my webapps/rails/nginx/logs/error.log

2012/03/04 12:01:01 [emerg] 15418#0: bind() to 0.0.0.0:13304 failed (98: Address already in use)
2012/03/04 12:01:01 [emerg] 15418#0: bind() to 0.0.0.0:13304 failed (98: Address already in use)
2012/03/04 12:01:01 [emerg] 15418#0: bind() to 0.0.0.0:13304 failed (98: Address already in use)
2012/03/04 12:01:01 [emerg] 15418#0: bind() to 0.0.0.0:13304 failed (98: Address already in use)
2012/03/04 12:01:01 [emerg] 15418#0: bind() to 0.0.0.0:13304 failed (98: Address already in use)
2012/03/04 12:01:01 [emerg] 15418#0: still could not bind()

The address that is in use is the port that my application is running on. Each time this happens, the identifier after [emerg] changes. Is anyone else seeing this? Any ideas why it's happening or how to fix it?

Thanks!