We measured energy distributions of electrons emitted in backward direction from sputter cleaned amorphous carbon foils under swift HCI bombardment. The shape of these spectra was found to depend strongly on the projectile charge qp (qp = 6 ... 39) for fixed velocity vp (vp = 19 atomic units, 9 MeV/u). We observe (for high projectile charge only) a K2VV hyper satellite line at 310 eV due to the double ionization of the K-shell in addition to the well known KVV peak of carbon (at 257 eV). From a careful analysis of the shape of these carbon Auger spectra including background subtraction and deconvolution techniques, we clearly observe a projectile charge dependence of the shape of the primary Auger electron spectrum. This effect is strongly connected to a modification of the electronic structure of the solid target at the moment of the Auger decay. We discuss different possible interpretations of this effect, such as an increase of the mean electronic temperature or a structural modification of the material.