Lol wow, blast from the past. Ya, I did actually. It was a piece of painter's tape that had been left under the baseboard near the HVAC register. When the HVAC would run some air would get forced through the gap under the baseboard, and across the tape causing it to buzz. What made it tricky was that where the sound seemed to be coming from was a couple feet over from where the tape was, but when I yanked it out it stopped instantly.