  High sensitivity Faraday rotation spectroscopy is used to measure the
fluctuating magnetization noise of non-interacting rubidium atoms under
resonant and non-resonant optical probing conditions. The spin noise frequency
spectra in dependence on the probe light detuning with respect to the
D2-transition reveals clear signatures of a coherent coupling of the
participating electronic levels. The results are explained by extended Bloch
equations including homogeneous and inhomogeneous broadening mechanisms. Our
measurements further indicate that spin noise originating from excited states
are governed at high intensities by collective effects.
