Note: Scott Cahill's wife has been the president of a construction company that specialized in dam inspections and repairs. An interesting "knowledge base" in a married expertise on dams.
As far as the "shock" vibrations felt on Kelly ridge & the pets responding with anxiety... this could be from the blasting.
Regarding a "hum", it would be useful if more information was described or provided by the locals. I always find credible pieces of information from locals that may be overlooked by "experts".
For example, UELF (ultra extremely low frequency), and upper harmonics, in a mechanical manifestation, are able to conduct long distances and create acoustic (sound) standing waves.
The Hyatt power plant is deep in the rock below Kelly ridge. If for example, the new refurbished and more efficient turbine just installed has blade geometries that create a new form of a harmonic at a 3600 rpm operation, the harmonics could couple to the rock foundation in multiple ways. One is via a cavity chamber resonance in a number of the physical geometries of the tunnels, the cavern, the piping, etc.
As UELF waves & some of the upper harmonics may not be detectable nearby (wavelengths in hundreds of feet at the velocity of the medium it travels within), these harmonics may be convergent in areas that end up affecting people as "sounds".
A restaurant & dance disco called "Earthquake Ethel's in Beaverton Oregon" would use a PDP-11 computer to coordinate the internal sound amplifiers & speakers in the building to resonate the building at its primary resonant frequency - thus re-creating a magnitude 3 equivalent shaking inside. It was cool. They did this every so often during the hours. However, the neighborhood residents were all up in arms as the acoustic sound waves from this effect developed at a distance away and would strongly resonate in different places in the neighborhood (wavelength convergence). Eventually, the residents complained enough to the city council and the restaurant closed.
If there was truly a "hum" effect going on, I would investigate it in a different way rather than immediately jumping to a complex phased array system thousands of miles away. (yes, I am familiar with these particular phased array systems - it is part of my research).
Just a note - typically, at least in the past, hydroelectric generators are designed to run at a much lower RPM than what you find with typical gas and steam turbines. Typically, a steam turbine generator is designed to run at either 3600 RPM (2-pole) or 1800 RPM (4-pole), but the hydro-electric generators I've seen have a much greater number of poles, and thus operate at considerably lower RPM.
I read that Hyatt generators run at 200 RPM, but that is unconfirmed. TVA's Raccoon Mountain Pumped Storage units operate at 300 RPM. A chart in the link below shows some typical hydro plant design RPM...
Speaking of “hum” and harmonics - true, but weird story - I bought a new UPS for my desktop computer a couple of years ago. The night after I first plugged it in, I started noticing a low-level low frequency (60 Hz) hum in the house. Not all the time, but the noise coincided with times when power demand was lighter. At times of higher demand, the noise doesn’t occur.
I have never been able to pin down a physical source of the hum; only that I first noticed it when I got the UPS. I think that there’s some connection between the noise and the UPS though. On the other hand, I have a 161,000 volt transmission line running across my property, about 250 feet away from the house. And a nuclear plant about 6 miles to my northeast. Now maybe the line is causing some standing waves, or maybe the voltage controlling circuits in the UPS are interacting with the household supply in some odd way.
It’s been an interesting phenomenon, but not bothersome enough to force me to do something about it. Just a curious oddity.
Reminds me of the harmonic booms coming from these low-riders with their volume and bass turned all the way up. You can feel the vibrations. Doors and windows rattling as they roll slowly down the street.