  We study the stress fluctuations in simulations of a two-dimensional
amorphous solid under a cyclic drive. It is known that this system organizes
into a reversible state for small driving amplitudes and remains in an
irreversible state for high driving amplitudes, and that a critical driving
amplitude separates the two regimes. Here we study the time series of the
stress fluctuations below and above the reversible-irreversible transition. In
the irreversible regime above the transition, the power spectrum of the stress
fluctuations is broad and has a $1/f^{\alpha}$ shape with $1< \alpha <2$. We
find that the low frequency noise power peaks near the stress at which dc
yielding occurs, which is consistent with the behavior expected in systems
undergoing a non-equilibrium phase transition.
