  Recently observed tunneling spectra on clean heavy fermion compounds show a
lattice periodic Fano lineshape similar to what is observed in the case of
tunneling to a Kondo ion adsorbed at the surface. We show that the translation
symmetry of a clean surface in the case of \emph{weakly correlated} metals
leads to a tunneling spectrum given by the superposition of the local weighted
density of states of all energy bands involved, which does not have a Fano
lineshape. In particular the spectrum will show any hybridization gap present
in the band structure. By contrast, in a \emph{strongly correlated} heavy
fermion metal the heavy quasiparticle states will be broadened by interaction
effects. The broadening grows as one moves away from the Fermi surface, up to a
value of the order of $T_K$, the Kondo scale. We show that the hybridization
gap is completely filled in this way, and an ideal Fano lineshape of width
$T_K$ results, similar to the impurity case. We also discuss the possible
influence of the tunneling tip on the surface, in (i) leading to additional
broadening of the Fano line, and (ii) enhancing the hybridization locally,
hence adding to the impurity type behavior. The latter effects depend on the
tip-surface distance.
