Perpendicular recording is believed to be one of the most promising candidates for the future generations of hard drives, because perpendicular recording is technically close to conventional longitudinal recording while it addresses the critical issue of thermal stability. A magnetic force microscopy (MFM) study of the data stability in a double-layer perpendicular magnetic recording medium is presented. Autocorrelation signal-to-noise ratio (ACSN) and more conventional signal-to-noise ratio (SNR) analysis were used in conjunction with MFM to characterize the integral noise characteristics of the written tracks. Transition noise, DC noise, and percolation effects were also studied to provide more detailed information on various sources of noise. Two types of media were investigated: CoCr-alloy based with relatively low remanent squareness of 0.7 and coercivity of 3.5 kOe and a Co/Pd based multilayer with remanent squareness of 1, coercivity field of 7 kOe and nucleation field of 3 kOe.