Since modern interferometers were designed to look for classical gravity waves (gravity waves are their sought “signal”), it
is reasonable to denominate as “noise” all test-mass-distance fluctuations that are not due to gravity waves. I adopt
terminology that reflects the original objectives of modern interferometers, even though it is somewhat awkward for the type of
quantum-spacetime-phenomenology studies discussed, in which interferometers would be used for searches of
quantum-gravity-induced distance fluctuations (and, therefore, in these studies quantum-gravity-induced distance fluctuations
would play the role of “signal”).