Only one of the switches is managed I believe. I've never really had cause to look at it. I obviously have work to do on that score, thanks. The router is a Cisco that's why I thought access point.
As it's netgear it could be a wireless\network card, but most likely some smartarse has plugged in a wireless access point.
As tom has pointed out your switches, if they are managed will be able to tell you which point has it plugged in. If you can't be arsed\don't have managed switches, you'll need to go walk around your site looking for a netgear wireless access point \ router \ or such plugged into your network.
Since the network monitor is only looking for a 10. range this seems possible. Thanks again I'll have a look for a Netgear tool.
As you've not had any DHCP issues, you've prob got a Wireless access point with a static ip on a different address (ie 192.168.1.x when your network is 10.0.0.x).
I believe there is a netgear search tool. Not sure tho.