App note from STMicroelectronics on high-side current sense RF noise filtering. Link here (PDF)
In an application such as a power supply or a DC-DC converter, the voltage output is generally noisy. Some spikes load the current. Alternatively, a temporary over voltage might occur creating either common mode or differential noise. Such high frequency signals may be demodulated by the current sensing device, resulting in an error in the current measurement.
Consequently, for power supply and DC-DC converter applications, it is necessary to filter the input path of the current sensing to improve the accuracy of the measurement. Such filters must be successfully implemented by choosing the right component values. If the wrong component values are selected, non-desired offset voltages and gain errors might be introduced, which compromise circuit performance.