Low frequency periodic signal

I observe a periodic, irregular, low-frequency signal 8-10 second duration, occurring 15 -20 times per day. Frequency in the range of 3-7 Hz

Screen Swhot 2023-02-10 at 2.12.34 PM

By irregular, I mean random (I think)
Does not seem to be airplane, train or helicopter.
My device is RD999 EHZ AM 00 in Palm Desert, CA
Other devices in the area seem to have similar signals, but not at the exact same time.
I have not checked devices in other areas.
Any ideas or suggestions?

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What does the frequency display look like?
There is no time scale on the screen grab, so difficult to estimate how long these last.

Maybe large trucks/earth-moving equipment? I saw something somewhat similar during the earth-moving/grading phase of a new development about a mile from me. One of the give-aways was that these started around 8am and finished at 5pm.

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Thanks for the response
This activity occurs at night as well during the day, so I don’t think it is earth-moving equipment.
I am hoping that this will be characteristic enough to allow ID.
Some more screen shots included, showing time scale and frequency display.


Michael, I am that other device in your area :slight_smile: I’m in Thousand Palms. I’ve had my shake running for years now. What you are seeing is indeed the freight trains passing your location along Interstate 10. Even know you are 1 to 2 miles from I-10 these Shake devices are very sensitive. If you were to analyze the pattern you’d see around a 5 minute time difference between your data and mine. That is the train traveling from you to me or vise-verse! :slight_smile: When I see my data increase I can often hear the faint low rumble of the train! I’m closer to I-10 than you, i see an increase in “noise” during the day that I associate it with the increase in Freeway traffic! Below is a perfect example, top me, bottom you, Train!