If the artifact were hardware failure — connector noise, thermal dropout, power fluctuation — then the interval would drift. Any physical failure mode that repeats has a tolerance range. Mechanical repetition accumulates error over time; the interval would be nine seconds on the first occurrence and nine-point-three or eight-point-eight on the third. It is nine, exactly, all three times. The only way to get that without drift is if the source of the artifact is not physical hardware. It is either digital — a process that fires on a precise timer — or it is a signal that was in the original audio environment when the recording was made.

A process firing on a precise timer would be software — something running on the recording device or on a network it was connected to. The recording device was in airplane mode. I checked the session logs after the fact. No network connections during the recording window. If it is software it is software installed on the device that runs offline. I have since factory reset the device. I cannot test that hypothesis on the original hardware anymore.

If the signal was in the audio environment — broadcast, physical, ambient — then something in the space where I was recording was producing a structured nine-second signal. I was in a parked car on a public street. I do not know what was producing that signal or why it would be structured. I know that structured signals in that frequency band require infrastructure to transmit. Infrastructure requires resources. Resources require decisions about what to monitor and when.