It seems it's triggered by files that don't have any audio:

(07:42:09) [0x17f0040] [rhythmdb_process_one_event] rhythmdb.c:2601: processing RHYTHMDB_EVENT_THREAD_EXITED
(07:42:09) [0x17f0040] [rhythmdb_process_one_event] rhythmdb.c:2575: processing RHYTHMDB_EVENT_STAT
(07:42:09) [0x17f0040] [rhythmdb_process_stat_event] rhythmdb.c:2125: queuing a RHYTHMDB_ACTION_LOAD: file:///home/darrenm/Music/Ash/intergalactic_sonic_7_s/burn.mp3
(07:42:09) [0x1a5bb30] [action_thread_main] rhythmdb.c:2963: executing RHYTHMDB_ACTION_LOAD for "file:///home/darrenm/Music/Ash/intergalactic_sonic_7_s/burn.mp3"
(07:42:09) [0x9d60b0] [rb_debug_init_match] rb-debug.c:211: Debugging enabled
(07:42:09) [0x9d60b0] [main] rb-metadata-dbus-service.c:517: initializing metadata service; pid = 26257; address = unix:tmpdir=/tmp
(07:42:09) [0x9d60b0] [rb_metadata_init] rb-metadata-gst.c:328: ogg vorbis tagging available
(07:42:09) [0x9d60b0] [rb_metadata_init] rb-metadata-gst.c:334: flac tagging available
(07:42:09) [0x9d60b0] [rb_metadata_init] rb-metadata-gst.c:340: id3 tagging available
(07:42:09) [0x9d60b0] [main] rb-metadata-dbus-service.c:536: D-BUS server listening on address unix:abstract=/tmp/dbus-vdl13mGVc6,guid=46bcede0334df05fb2d078344b989ed1
(07:42:09) [0x1a5bb30] [start_metadata_service] rb-metadata-dbus-client.c:296: Got metadata helper D-BUS address unix:abstract=/tmp/dbus-vdl13mGVc6,guid=46bcede0334df05fb2d078344b989ed1
(07:42:09) [0x1a5bb30] [start_metadata_service] rb-metadata-dbus-client.c:312: Metadata process 26257 started
(07:42:09) [0x9d60b0] [_new_connection] rb-metadata-dbus-service.c:383: new connection to metadata service
(07:42:09) [0x1a5bb30] [start_metadata_service] rb-metadata-dbus-client.c:329: sending metadata saveable types query
(07:42:09) [0x9d60b0] [_handle_message] rb-metadata-dbus-service.c:353: handling metadata service message: getSaveableTypes
(07:42:09) [0x1a5bb30] [start_metadata_service] rb-metadata-dbus-client.c:352: saveable types from metadata helper: application/ogg, application/x-id3, audio/mpeg, audio/x-vorbis, audio/x-flac
(07:42:09) [0x1a5bb30] [rb_metadata_load] rb-metadata-dbus-client.c:481: sending metadata load request
(07:42:09) [0x9d60b0] [_handle_message] rb-metadata-dbus-service.c:353: handling metadata service message: load
(07:42:09) [0x9d60b0] [rb_metadata_dbus_load] rb-metadata-dbus-service.c:126: loading metadata from file:///home/darrenm/Music/Ash/intergalactic_sonic_7_s/burn.mp3
(07:42:09) [0x9d60b0] [rb_metadata_load] rb-metadata-gst.c:732: loading metadata for uri: file:///home/darrenm/Music/Ash/intergalactic_sonic_7_s/burn.mp3
(07:42:09) [0x9d60b0] [rb_metadata_load] rb-metadata-gst.c:780: going to PAUSED for metadata, uri: file:///home/darrenm/Music/Ash/intergalactic_sonic_7_s/burn.mp3
(07:42:09) [0x9d60b0] [rb_metadata_gst_typefind_cb] rb-metadata-gst.c:489: found type application/x-id3
(07:42:09) [0x9d60b0] [rb_metadata_bus_handler] rb-metadata-gst.c:676: message of type state-changed from fakesink
(07:42:09) [0x9d60b0] [rb_metadata_bus_handler] rb-metadata-gst.c:676: message of type state-changed from fakesink
(07:42:09) [0x9d60b0] [rb_metadata_bus_handler] rb-metadata-gst.c:676: message of type state-changed from typefind
(07:42:09) [0x9d60b0] [rb_metadata_bus_handler] rb-metadata-gst.c:676: message of type state-changed from decodebin
(07:42:09) [0x9d60b0] [rb_metadata_bus_handler] rb-metadata-gst.c:676: message of type state-changed from urisrc
(07:42:09) [0x9d60b0] [rb_metadata_bus_handler] rb-metadata-gst.c:676: message of type state-changed from pipeline
(07:42:09) [0x9d60b0] [rb_metadata_bus_handler] rb-metadata-gst.c:676: message of type state-changed from id3demux0
(07:42:09) [0x9d60b0] [rb_metadata_bus_handler] rb-metadata-gst.c:676: message of type state-changed from id3demux0
(07:42:09) [0x9d60b0] [rb_metadata_handle_missing_plugin_message] rb-metadata-gst.c:568: got missing-plugin message from decodebin: gstreamer|0.10|rhythmbox-metadata|ID3 tag demuxer|decoder-application/x-id3
(07:42:09) [0x9d60b0] [rb_metadata_gst_get_missing_plugin_type] rb-metadata-gst-common.c:244: missing plugin is a container demuxer
(07:42:09) [0x9d60b0] [rb_metadata_bus_handler] rb-metadata-gst.c:614: got error message from decodebin
(07:42:09) [0x9d60b0] [rb_metadata_bus_handler] rb-metadata-gst.c:630: caught error: A ID3 tag demuxer plugin is required to play this stream, but not installed. 
(07:42:09) [0x9d60b0] [rb_metadata_load] rb-metadata-gst.c:805: failed to go to PAUSED for file:///home/darrenm/Music/Ash/intergalactic_sonic_7_s/burn.mp3
(07:42:09) [0x9d60b0] [rb_metadata_dbus_load] rb-metadata-dbus-service.c:128: metadata load finished (type application/x-id3)
(07:42:09) [0x9d60b0] [rb_metadata_get_missing_plugins] rb-metadata-gst.c:1219: adding [gstreamer|0.10|rhythmbox-metadata|ID3 tag demuxer|decoder-application/x-id3,ID3 tag demuxer] to return data
(07:42:09) [0x9d60b0] [rb_metadata_dbus_load] rb-metadata-dbus-service.c:173: metadata error: A ID3 tag demuxer plugin is required to play this stream, but not installed.
(07:42:09) [0x9d60b0] [rb_metadata_dbus_add_to_message] rb-metadata-dbus.c:132: opening container type {uv}
(07:42:09) [0x1a5bb30] [rb_metadata_load] rb-metadata-dbus-client.c:517: missing plugins; killing metadata service to force registry reload
(07:42:09) [0x1a5bb30] [kill_metadata_service] rb-metadata-dbus-client.c:149: closing dbus connection
(07:42:09) [0x1a5bb30] [kill_metadata_service] rb-metadata-dbus-client.c:159: killing child process
(07:42:09) [0x1a5bb30] [kill_metadata_service] rb-metadata-dbus-client.c:166: closing metadata child process stdout pipe
(07:42:09) [0x1a5bb30] [rb_metadata_load] rb-metadata-dbus-client.c:526: has audio: 1
(07:42:09) [0x1a5bb30] [rb_metadata_load] rb-metadata-dbus-client.c:535: has video: 0
(07:42:09) [0x1a5bb30] [rb_metadata_load] rb-metadata-dbus-client.c:544: has other data: 0
(07:42:09) [0x1a5bb30] [rb_metadata_load] rb-metadata-dbus-client.c:552: got mimetype: application/x-id3
(07:42:09) [0x17f0040] [rhythmdb_process_one_event] rhythmdb.c:2579: processing RHYTHMDB_EVENT_METADATA_LOAD
(07:42:09) [0x17f0040] [rhythmdb_process_metadata_load] rhythmdb.c:2470: missing plugins during metadata load for file:///home/darrenm/Music/Ash/intergalactic_sonic_7_s/burn.mp3
Rhythmbox-Message: Missing plugin: gstreamer|0.10|rhythmbox-metadata|ID3 tag demuxer|decoder-application/x-id3
(07:42:09) [0x17f0040] [missing_plugins_event] rb-missing-plugins.c:226: gst_install_plugins_async() result = 200
(07:42:09) [0x17f0040] [rhythmdb_process_metadata_load] rhythmdb.c:2480: processing missing plugins

When looking at the file using 'file' it returns this:

Music/Ash/intergalactic_sonic_7_s/burn.mp3: Audio file with ID3 version 2.4.0, contains: 

as opposed to a normal MP3 file:

Music/Alanis_Morissette/Jagged_Little_Pill/01.All_I_Really_Want.mp3: Audio file with ID3 version 2.3.0, contains: MPEG ADTS, layer III, v1, 192 kbps, 44.1 kHz, JntStereo

When trying to play the file in mplayer, it seems to be empty. I deleted the file and the problem went away.