Noise spectroscopy as a highly sensitive method for non-destructive diagnostics of semiconductor devices was applied to solar cells based on crystalline silicon with a view to evaluating the quality and reliability of this solar cell type. The experimental approach was used in a reverse-biased condition where the internal structure of solar cells, as well as pn-junction itself, was electrically stressed and overloaded by a strong electric field. This gave rise to a strong generation of a current noise accompanied by local thermal instabilities, especially in the defect sites. It turned out that local temperature changes could be correlated with generation of flicker noise in a wide frequency range. Furthermore, an electrical breakdown in a nonstable form also occurred in some specific local regions what created micro-plasma noise with a two-level current fluctuation in the form of a Lorentzian-like noise spectrum. The noise research was carried out on both of these phenomena in combination with the spectrally-filtered electroluminescence mapping in the visible/near-infrared spectrum range and the dark lock-in infrared thermography in the far-infrared range. Then the physical origin of the light emission from particular defects was searched by a scanning electron microscope and additionally there was performed an experimental elimination of one specific defect by the focused ion beam milling.