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The microscopic mechanism of charge instabilities and the formation of inhomogeneous states in systems with strong electron correlations is investigated. We demonstrate that within a strong coupling expansion the single-band Hubbard model shows an instability towards phase separation and extend the approach also for an analysis of phase separation in the Hubbard-Kanamori hamiltonian as a prototypical multiband model. We study the pairing fluctuations on top of an inhomogeneous stripe state where superconducting correlations in the extended <i>s</i>-wave and <i>d</i>-wave channels correspond to (anti)bound states in the two-particle spectra. Whereas extended <i>s</i>-wave fluctuations are relevant on the scale of the local interaction parameter <i>U</i>, we find that <i>d</i>-wave fluctuations are pronounced in the energy range of the active subband which crosses the Fermi level. As a result, low energy spin and charge fluctuations can transfer the <i>d</i>-wave correlations from the bound states to the low energy quasiparticle bands. Our investigations therefore help to understand the coexistence of stripe correlations and <i>d</i>-wave superconductivity in cuprates.