Noise disturbances often require a bit of a detective work, but every once and a while something crops up that makes you go, “Hmmm…”

Let’s call this “The Case of the Rumble and the Rat.”

We did some work with a small recording studio built in yet another repurposed industrial building. This kind of structure usually poses design challenges, often involving how to upgrade the existing infrastructure for electrical and mechanical systems.

But this story had a different twist: The owner had called us to investigate a noise problem in their control room that hadn’t been there until recently. As he put it:

“Kind of a ‘whump,’ … ‘whump’ … then just a constant rumble.”

There could have been any number of sources for the noise. Was there something outside the building? Was it coming from a stairwell, or an adjacent tenant? What about the HVAC equipment, or the plumbing, or even something related to the monitoring system? We scoured the space checking things out one by one.

The last place we looked was (of course) the last place we looked. As we opened the door to a mechanical closet, it was clear that the noise was emanating from the air handler. We opened the access panel on the unit and, lo and behold, our culprit was obvious: the body of a deceased rat making the rounds on the, er, squirrel cage fan.

Like a tennis shoe in the dryer, when the fan came on there would be a couple of thumps as the body dropped. Eventually centripetal force took over and pinned it to the perimeter of the fan, which threw the fan out of balance and generated the low-frequency rumble.

One rodent extraction later – and a little future-proofing by an exterminator – we moved on to the next (and less zoological) acoustical detective case.