I've had about 48 hours of extremely high CPU usage on my main MySQL database for no apparent reason.

I realize this question is quite similar to the one posed here: http://dba.stackexchange.com/questions/20225/high-cpu-usage-from-mysql-with-no-queries-at-all-running

However, this MySQL server does not have ntp installed at all, and as the leap-second bug is from a few months ago, I don't think that's the explanation. 

SHOW PROCESSLIST does not show any long-running processes/queries, and there have been no recent changes to DB schema, etc. 

The server is also extremely locked down so that only other application servers within the VPN may access it, and has plenty of RAM (17 GB) which is not maxed out either.

Is there anything else that I should look into, or any other common causes of high CPU?

The server is an EC2 m2.xlarge instance: 17.1 GB RAM, 6.5 EC2 "Compute Units" with this configuration:

    
    user		= mysql
    socket		= /var/run/mysqld/mysqld.sock
    port		= 3306
    basedir		= /usr
    datadir		= /var/lib/mysql
    tmpdir		= /tmp
    skip-external-locking

    key_buffer		= 256M
    sort_buffer_size 	= 16M
    read_buffer_size 	= 16M
    max_allowed_packet	= 32M
    thread_stack		= 192K
    thread_cache_size       = 8

    max_connections        = 200
    thread_concurrency     = 12

    query_cache_limit	= 4M
    query_cache_size        = 128M

    log_error                = /var/log/mysql/error.log

    log_slow_queries	= /var/log/mysql/mysql-slow.log
    long_query_time = 2
    log-queries-not-using-indexes

    server-id		= 1
    log_bin			= /var/lib/mysql/mysql-bin.index
    expire_logs_days	= 10
    max_binlog_size         = 1000M
    sync_binlog		= 1

    innodb_data_file_path 	= ibdata1:2000M;ibdata2:10M:autoextend
    innodb_buffer_pool_size = 11G
    innodb_additional_mem_pool_size = 128M
    innodb_log_file_size 	= 1000M
    innodb_log_buffer_size 	= 32M
    innodb_flush_log_at_trx_commit = 1
    innodb_lock_wait_timeout = 50