The proposed model allows to analyze reasons for surface enhanced Raman scattering (SERS) by molecules adsorbed onto surface of metal particles. It considers multiple inelastic scattering of a photon, which moves along a closed loop inside a system of closely packed small metallic particles. During this motion, the photon undergoes multiple exchanges with the medium by the same amount of energy corresponding to excitation in the system of charge density fluctuations, which are permanently present in the system. The energy of such fluctuations can be an arbitrary value, with magnitude of less than the energy of incident photon. Probability of the excitation is very high and comparable with the probability of resonance excitation of the dipole surface plasmon in a separate particle. Strong local fields related to these fluctuations exist over entire frequency range from infrared up to ultraviolet. The reason for the photon motion along the closed loop is related to constructive interference of amplitudes corresponding to two alternative ways of the loop passing; clockwise and counter clockwise. Probability of such motion is calculated. Peculiarities of behavior of charge density fluctuations allow explaining some specific features of flicker noise. Copyright © 2013 John Wiley & Sons, Ltd.