We observed the second harmonic voltage response of pseudo-spin valves subjected to currents oscillating at frequencies in the sub-kilohertz range. Peaks appear in its magnetic field dependence, with a signal-to-noise ratio equal to or greater than the magnetoresistance response of the same samples. This signal is interpreted as arising from the response of the magnetization to the spin torque induced by current when the magnetic layers are in non-collinear orientations. Thus, the method probes the current susceptibility of the magnetization which is shown to be sensitive to non-collinear states undetectable in the magnetoresistance.