Some IRC servers do a sort of port scan on connect. If you look closely at the MOTD when you connect to the server, you might find something similar to this:
--- - Please be aware that OFTC operates an open proxy detection
--- - system(http://www.blitzed.org/bopm). Please disregard
--- - connections from proxy-scan.oftc.net(18.104.22.168) as it
--- - is the detector in action. If you dislike this, please
--- - disconnect now.
Anything on port 6667 will most likely be the IRC proxy scans. Its nothing to be worried about, unless of course, you're not using IRC