First observations of an unusual oscillatory instability in a binary metallic fluid exhibiting liquid-liquid phase separation are reported. For this aim, the liquid/vapour interface of the Ga0.95Pb0.05 alloy has been studied by a surface sensitive optical second harmonic generation (SHG) probe over a wide temperature range (465-313 degreesC) at conditions above and inside the miscibility gap. Regular oscillations of the SHG intensities with a period of similar to40 min are found, which correlate strongly with temperature oscillations of the bulk fluid with amplitudes of similar to5-8 K. It is shown that these oscillations are driven by wetting and dewetting characteristics at the interface during phase separation via a periodic variation of the interfacial emissivities. A qualitative explanation of the surface induced bulk instabilities is presented. (C) 2004 Elsevier B.V. All rights reserved.