1. A method of filtering out pressure noise generated by one or more piston pumps, where each pump is connected to a common downstream piping system, and where the discharge pressure is measured by a pressure sensitive gauge, wherein the instantaneous angular position(s) of the pump(s)' crankshaft or actuating cam is/are measured simultaneously with the discharge pressure and used as fundamental variables in an adaptive mathematical noise model, and wherein the adaptive mathematical noise model comprises a theoretical part and an empirical part, the theoretical part representing the expected flow and pressure fluctuations that, for each new pressure measurement, are calculated on the basis of the associated measured angular positions and knowledge of piston speeds, valve characteristics, the compressibility of the fluid and the geometry of the downstream piping system, and the empirical part, which describes discrepancies between measured and expected noise, being calculated as frequently as the theoretical one but being represented by periodically updated model parameters.