  In low-disorder, two-dimensional electron systems (2DESs), the fractional
quantum Hall states at very small Landau level fillings ($\nu$) terminate in a
Wigner solid (WS) phase, where electrons arrange themselves in a periodic
array. The WS is typically pinned by the residual disorder sites and manifests
an insulating behavior, with non-linear current-voltage (\textit{I-V}) and
noise characteristics. We report here, measurements on an ultra-low-disorder,
dilute 2DES, confined to a GaAs quantum well. In the $\nu < 1/5$ range,
superimposed on a highly-insulating longitudinal resistance, the 2DES exhibits
a developing fractional quantum Hall state at $\nu=1/7$, attesting to its
exceptional high quality, and dominance of electron-electron interaction in the
low filling regime. In the nearby insulating phases, we observe remarkable
non-linear \textit{I-V} and noise characteristics as a function of increasing
current, with current thresholds delineating three distinct phases of the WS: a
pinned phase (P1) with very small noise, a second phase (P2) in which $dV/dI$
fluctuates between positive and negative values and is accompanied by very high
noise, and a third phase (P3) where $dV/dI$ is nearly constant and small, and
noise is about an order of magnitude lower than in P2. In the depinned (P2 and
P3) phases, the noise spectrum also reveals well-defined peaks at frequencies
that vary linearly with the applied current, suggestive of washboard
frequencies. We discuss the data in light of a recent theory that proposes
different dynamic phases for a driven WS.
