Carbon films deposited (at elevated temperatures) on SERS active metal substrates show remarkable fluctuations in Raman spectra, if a Raman microscope is used. In subsequently recorded spectra distinct sets of intense, but rather narrow Raman lines appear, which are related to vibrations of corresponding carbonaceous groups. These spectral fluctuations evidence an enduring surface chemistry producing a variety of carbon chain configurations, which get temporarily in contact with metal sites, the so-called 'hot spots', that exhibit extremely large surface enhancements.