  Using the example of the rare decay $B \to X_s \gamma$, we analyse the
importance of interference effects for the bounds on the parameters in the
squark mass matrices within the unconstrained MSSM. In former model-independent
analyses no correlations between the different sources of flavour violation
were taken into account. In our new analysis we include the contributions from
charged Higgs bosons, charginos and neutralinos and their interference effects
and, even more important, the effects that appear when several flavour
violating parameters, i.e. several off-diagonal elements in the squark mass
matrices, are switched on simultaneously. We derive new bounds on certain
off-diagonal elements of the squark-mass matrix which are in general one order
of magnitude weaker than the previous bounds.
