Wireless access point being hacked?

[Nocky24]

My router keeps showing a device on my network which isn't mine, but gets an assigned ip from my router. It only shows up occasionally though. When i first noticed it i think i was just using WEP security so i deleted the assigned ip for the unknown device and upped the security to wpa2 with a new password. However now the unknown assigned ip is back again showing up as 'active' on my router stats and then when i pull the plug on my wireless access point it then shows up as 'inactive' so im pretty sure its using the wireless access point. By the way i know its an unknown device as all my known network devices have reserved ips on the router and have been named.

I've also been getting an extremely high number of disconnections and line noise on my line, would this have anything to do with it? I can't see how myself, but me and my isp are really struggling to find reasons for it.

Any ideas on what i can do? Please help

---By the way im with O2 broadband on the 20mb package using a wireless II box (firmware 7.4.20.5) and my wireless access point is a netgear wg602v4, the wireless is also turned OFF on the o2 wireless II box so its not that. My network setup is via one ethernet port on my router to a series of homeplugs and network switches + the one netgear wireless access point.

 

[Nocky24]

Just what I was thinking. What's the name of the device that's showing up?

It shows up as something like Unknown device 1354-2564-2876. Its not coming up now as i've been keeping the access point turned off for now. Still getting lots of disconnections though, got over 70 today o2 told me and that was at the test socket with the router plugged into a filter. Probably going to need to get an engineer out as i get a lot of noise on the line particularly when the nets up and running.