  Unstable electrostatic resistive modes, driven by density gradients, are
identified in a bounded sheared slab. The boundary conditions play a crucial
role and are shown to change the nature of the problem, which is related to so
called "universal" mode. The dispersion relation and the structure of the
eigenmodes of the instability are derived and are shown to depend on a limited
set of dimensionless parameters. The occurrence and possible impact of these
modes on numerical simulations and actual plasmas are discussed.
