Someone's bugging me...

I have a small group of coworkers that I speak with privately on numerous politics of the workplace. Some of these are warranted, some are not, either way they are in private. Lately it has been brought to my attention that our conversations are being overheard. It's not by someone standing outside my door or around the corner so how are they listening in? We came to the assumption, not yet confirmed, but pretty sure that someone has bugged my office. I'm going to do a sweep tomorrow (Friday) using the project of painting my office as a cover. This way no one will suspect why I'm behind cabinets or up in the ceiling. I'm really agitated now and getting more so as I think about it. Today I will fester, tomorrow I will conquer.