  We investigate the extreme X-ray variability of a z = 1.608 active galactic
nucleus in the 7 Ms Chandra Deep Field-South (XID 403), which showed two
significant X-ray brightening events. In the first event, XID 403 brightened by
a factor of $>2.5$ in $\lesssim6.1$ rest-frame days in the observed-frame 0.5-5
keV band. The event lasted for $\approx5.0\textrm{-}7.3$ days, and then XID 403
dimmed by a factor of $>6.0$ in $\lesssim6.1$ days. After
$\approx1.1\textrm{-}2.5$ years in the rest frame (including long observational
gaps), it brightened again with the 0.5-5 keV flux increasing by a factor of
$>12.6$. The second event lasted over 251 days and the source remained bright
until the end of the 7 Ms exposure. The spectrum is a steep power law (photon
index $\Gamma=2.8\pm0.3$) without obscuration during the second outburst, and
the rest-frame 2-10 keV luminosity reaches $1.5^{+0.8}_{-0.5}\times10^{43}$ erg
s$^{-1}$; there is no significant spectral evolution within this epoch. The
infrared-to-UV spectral energy distribution of XID 403 is dominated by the host
galaxy. There is no significant optical/UV variability and $R$-band (rest-frame
$\approx2500$ $\unicode{xC5}$) brightening contemporaneous with the X-ray
brightening. The extreme X-ray variability is likely due to two X-ray unveiling
events, where the line of sight to the corona is no longer shielded by
high-density gas clumps in a small-scale dust-free absorber. XID 403 is
probably a high-redshift analog of local narrow-line Seyfert 1 galaxies, and
the X-ray absorber is a powerful accretion-disk wind. On the other hand, we
cannot exclude the possibility that XID 403 is an unusual candidate for tidal
disruption events.
