Unknown Wireless Access Point in my Company???

Good Day,
I have picked up an SMC access point’s signal in my company. I don’t know were its coming from and it is interferring with my wireless laptops connected to my LAN. I have a 3COM and a Cisco WAP setup now. I would like to find some type of hardware/software to trace this unknown AP and somehow block its signal. We have a BIG 2 story building and the AP signal is strongest in the middle of the 2nd floor?? I’d understand if it was strongest at the corner of the building, that would mean that the Building next door had an AP setup and we’d get some of the signal… Please help… Thank you!