Telephone switches have a distinctive sound. The clicks and clacks are very sharp and distinctive.
While an ESS switch is silent (except for the noisy blowers), there may be some nearby support racks that do contain relays, and those relays will make the sharp clack sounds.
As to the sound of emergency generators, they are noisy. I was passing a nursing home when they were testing their generator and it was loud!
Places with critical functions likes hospitals and nursing homes have backup power generators. They are tested every so often. Sometimes power failures result from failure of the switchgear to transition from one source to another. One of my employer's location had a backup source and they did a test; they were out of commission the whole day due to failures of the control circuitry.
Electric power control circuitry is pretty amazing to me. It must handle -- live -- tremendous amounts of current.
The power system today is pretty fancy and duplicated which means power failures are quiten uncommon even when one piece gets hit by lightning. Unfortunately, it is so interconnected that a bad failure will ripple and make a big mess. It happened in 1965 causing the big NE blackout and again not too long ago causing another NE blackout.
Unfortunately, once large segments go out, it takes a while to bring them all back online; they can't flip a switch and do a whole city at once. Also, once a power plant itself goes off line, it takes a while to build back up.
I wish there was some cost-efficient practical manner of "buffering" large amounts of power for brief moments to avoid huge surges that cause everything to shut down. If the safety breakers are too sensitive there will be too many false trips causing unnecessary problems. If the breakers aren't sensitive enough surges will ripple through.
The 1965 NE power failure has been documented as to causes and solutions (which presumably have been implemented). But I don't know if they ever published the analysis of the more recent NE power failure. I believe it was caused by surges in an Ohio system that rippled to other systems. I don't know if there is a protection against such "rippling". That's why I wish there were some kind of "buffers".