An analysis of noise in passive sampling mixers is presented, which is based on derivations of auto- and cross-correlation functions that capture statistical co-dependence of noise components during the tracking and hold phases of sampling mixer operation. This study accurately predicts the noise-folding due to cyclostationarity of the sampling noise of the mixer. As will be discussed, notwithstanding its simple form, the proposed approach yields an accurate noise model, which will simplify to existing noise models presented by prior work under their adopted assumptions.