  Here we propose several methods with increasing precision for analytically
estimating white noise squeezing in the frequency domain of classical
parametrically-driven resonators with added noise. The analytical model is
based on obtaining the response of the resonator to the added noise using
Green's function. The response consists of three parts: elastic, down, and up
parametric conversions. We obtain the Green's function approximately using the
first-order averaging method or exactly, in principle, using Floquet theory. We
characterize the noise squeezing by calculating the statistical properties of
the real and imaginary parts of the Fourier transform of the resonator response
to added noise. Furthermore, we observe that the squeezing effects occur only
at half the parametric pump frequency. Due to correlation, the squeezing limit
of $-6$~dB can be reached even with detuning around resonance near the
instability threshold. Additionally, we validate some of our theoretical
predictions of squeezing with the results obtained from the numerical
integration of the stochastic differential equations of our model. We also
applied our techniques to investigate squeezing in a pair of coupled parametric
and harmonic resonators with a single noise input. The results obtained from
Floquet theory can be applied generally to coupled
