  Stochastic noise estimator method is a powerful tool to calculate the
disconnected insertion involving quark loops. We study the variance reduction
technique with unbiased subtraction. We use the complex $Z_2$ noise to
calculate the quark loops on a $16^3 \times 24$ lattice with $\beta = 6.0$ and
$\kappa$ = 0.154. Unbiased subtraction method is performed by using hoping
parameter expansion. We report on the variance reduction for the point-split
vector current as a function of the number of subtraction terms and the number
of noise used.
