  In gravitational-wave interferometers, test masses are suspended on thin
fibers which experience considerable tension stress. Sudden microscopic stress
release in a suspension fiber, which I call a 'creep event', would excite
motion of the test mass that would be coupled to the interferometer's readout.
The random test-mass motion due to a time-sequence of creep events is referred
to as 'creep noise'. In this paper I present an elasto-dynamic calculation for
the test-mass motion due to a creep event. I show that within a simple
suspension model, the main coupling to the optical readout occurs via a
combination of a "dc" horizontal displacement of the test mass, and excitation
of the violin and pendulum modes, and not, as was thought previously, via
lengthening of the fiber. When the creep events occur sufficiently frequently
and their statistics is time-independent, the creep noise can be
well-approximated by a stationary Gaussian random process. I derive the
functional form of the creep noise spectral density in this limit, with the
restrictive assumption that the creep events are statistically independent from
each other.
