I would have to say the UPS is creating havoc, in the form of Harmonic Distortion.
When tracing Circuits via my Amprobe-Pascar Circuit Tracer, the audible sound plus received signal would be extremely distorted on UPS Circuits.
The Circuit Tracer mentioned above, functions by Modulating the 60 Hz AC Circuit's Fundamental with a ± 2kHz signal (tone).
The Transmitter is connected at the location to be traced - and uses the 60 Hz Fundamental as the Carrier Wave.
The Receiver is normally used at a Breaker/Fuse, but may be used elsewhere. It picks up the tone via Inductive Coupling on the test circuit.
Normally, the received tone and scaled levels are crisp and clear.
However, when testing UPS circuits, the tone + scaled levels are very distorted.
Also, they become "distributed" around common circuits (like remaining two circuits of multiwire circuits, or same phases in panelboard, which are multiples of three in location numbers).
If the tester reacts this way, imagine what is being pressed against the Genny!
Just a hunch!
p.s. Ironically, the work being done in the above scenario (along with nearly 95% of projects between 1990 and 2002), was in the Banking Industry.