We just finished added a bathroom upstairs. There was previously one bathroom downstairs Recently I was getting ready in the morning and heard a stange intermittent buzzing. Buzzing for 1 second, silence for 3/4, then buzzing for 1 second, etc. My roommate was downstairs getting ready with her boyfriend. I assumed he was using an electric razor and the sound was translating up from below through the drain lines. However, I heard it again this morning and he wasn't here. I went downstairs to discover that my roommate was using her shower. The sound upstairs seemed to stop as soon as she turned the water off downstairs. Do I have a plumbing problem, or is this just a new idiosyncrasy? 
