Sliding correlators are frequently used in the acquisition of pseudonoise sequences in spread-spectrum and ranging systems. High-speed acquisition is often required. The paper examines the decorrelation between the received and locally generated codes and the increase in self-generated noise at the output of the correlator as the search rate is increased. A numerical approach enables the analysis to be carried out for search rates well in excess of 1 bit per sequence period. It is found that decorrelation and self-noise place an upper bound on the search rate of the synchroniser, which has been ignored previously. The analysis has been carried out for a range of code lengths, and analytic expressions are obtained for both decorrelation and self-noise terms, which enable the effects to be estimated by extrapolation for other, longer, codes, where the effects are more pronounced. The results enable a correction factor to be incorporated into the expression for the maximum search rate of a sliding correlator under external noise conditions.