  In addition to the well-known 11-year solar cycle, the Sun's magnetic
activity also shows significant variation on shorter time scales, e.g. between
one and two years. We observe a quasi-biennial (2-year) signal in the solar
p-mode oscillation frequencies, which are sensitive probes of the solar
interior. The signal is visible in Sun-as-a-star data observed by different
instruments and here we describe the results obtained using BiSON, GOLF, and
VIRGO data. Our results imply that the 2-year signal is susceptible to the
influence of the main 11-year solar cycle. However, the source of the signal
appears to be separate from that of the 11-year cycle. We speculate as to
whether it might be the signature of a second dynamo, located in the region of
near-surface rotational shear.
