One thing we knew going into this investigation is that acoustic interference can occur where you least expect it. Several years ago, Fu became annoyed by an ear-piercing sound coming from a lightbulb in his apartment. He took spectral measurements and noticed that the lightbulb tended to shriek when the air conditioner turned on. He eventually concluded that the compressor was pumping coolant through its pipes at the same resonant frequency of the filament in the bulb. Normally, this wouldn't be a problem. But in this case, the coolant pipes ran through the ceiling and mechanically coupled to the ceiling joist supporting the lightbulb. The superintendent opened up the ceiling and separated the joist from the pipe with a piece of duct tape, to dampen the unwanted coupling. The sound stopped.