  The frequencies of solar oscillations are known to change with solar
activity. We use Principal Component Analysis to examine these changes with
high precision. In addition to the well-documented changes in solar normal mode
oscillations with activity as a function of frequency, which originate in the
surface layers of the Sun, we find a small but statistically significant change
in frequencies with an origin at and below the base of the convection zone. We
find that at r=(0.712^{+0.0097}_{-0.0029})R_sun, the change in sound speed is
\delta c^2 / c^2 = (7.23 +/- 2.08) x 10^{-5} between high and low activity.
This change is very tightly correlated with solar activity. In addition, we use
the splitting coefficients to examine the latitudinal structure of these
changes. We find changes in sound speed correlated with surface activity for r
>~ 0.9R_sun.
