  The dc voltage observed at low-temperatures in a 2D electron sample $without$
external excitation is accounted by the Schottky contact rectification of the
noise generated in the measuring circuit. The rectified voltage is shown to
depend on the asymmetry of the contact pair. The dependence of the rectified
voltage on the noise amplitude first follows the trivial quadratic law, then
exhibits a nearly linear behavior, and, finally, levels-off.
