What’s that sound? Probe tones and poltergeists: Two case studies in diagnosing noise sources
Kenneth A. Cunefare · The Journal of the Acoustical Society of America · 2016
Case #1: Following construction of a new hospital building within a larger campus, residents began to complain about droning noises in the surrounding neighborhood. Blame was laid on HVAC chillers and an MRI chiller installed on exposed roof-tops of the building. However, there were numerous other chillers on buildings on the campus that were not blamed; a test using probe tones eliminated the hospital building as the source impacting the community. Case #2: A homeowner complained of intermittent groaning and moaning noises in the home (poltergeist-like). Interviews revealed that the noises occurred essentially randomly; while the homeowner correlated occurrences to whether or not it had recently rained, the correlation was weak. Additionally, the homeowner had found that opening a water tap would cause the sound to fade away; this was suggestive, but since the sound faded away in a short time even without opening the valve, it was not definitive. Complicating the diagnosis was the intermittency of the noise (weeks could pass between events), and its short duration. A faulty GFI threw a red-herring into the mix, but ultimately the problem was solved by replacing the household water pressure regulator.