The continuum spectrum of noise found in the power spectra of Doppler shift measurements of the Sun provides information concerning non-oscillatory effects in the photosphere and forms a background against which oscillation modes must be detected. A proper determination of the continuum spectrum requires the genuine solar signal to be identified from amongst a number of instrumental effects. A number of authors have used cross-spectra form from simultaneous data sets to help to achieve such identification. In this paper we build on recent advances in the understanding of the noise characteristics of resonant scattering spectrometers to develop alternative techniques for isolating and evaluating solar and different instrumental noise contributions. Brief analyses of simulated data and BiSON measurements are presented to illustrate the potential of the techniques. helioseismology; noise level.