[CentOS] MySQL ERROR - UNKNOWN_MYSQL_USER

This is strange behavior because as soon as I start mysqld 
with a clean error log, I get the following messages:

110720 21:38:47 [Note] /usr/libexec/mysqld: ready for 
connections.
Version: '5.5.14-log'  socket: '/var/lib/mysql/mysql.sock'
port: 2500  MySQL Community Server (GPL) by Remi

110720 21:38:48 [Warning] Access denied for user 
'UNKNOWN_MYSQL_USER'@'localhost' (using password: NO)

The strange things is, AFAIK there are no clients trying to 
connect to mysql. I shutdown a mysql CLI monitor I had 
running, and did the restart again.

So I'm just wondering why I get this message, when AFAIK 
there is nothing that should be trying to connect to mysql - 
unless it's a server daemon running somewhere?

Has anyone else come across this funny error message?

Kind Regards,

Keith Roberts

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