Speciality: syslogd is configured to receive external messages from Cisco router. Sometimes (may take a week) under high load named hangs until its restart. strace -p <named_pid> says: send(3,"<syslog message> After disabling of receiving of external messages by syslogd all work just fine. Possible problem: syslog resolves IP to name for external message, but named is busy by sending message to syslog in that time.
btw, rpm -q bind sysklogd : bind-8.2.2_P7-0.6.2 sysklogd-1.3.31-17
This will be fixed in sysklogd-1.4-4, which will be in the next rawhide release; you will be able to start syslogd with the '-x' option that disables reverse lookups of incoming messages.