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 _ { \odot } , the change in sound speed is \delta c ^ { 2 } / c ^ { 2 } = ( 7.23 \pm 2.08 ) \times 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 \gtrsim 0.9 R _ { \odot } .