  The energy, momentum and temperature dependence of the quasiparticle local
density of states (LDOS) of a two-dimensional $d_{x^2-y^2}$-wave superconductor
with random disorder is investigated using the first-order T-matrix
approximation. The results suggest that collective modes such as spin/charge
density waves are relevant low-energy excitations of the cuprates that
contribute to the observed LDOS modulations in recent scanning tunneling
microscopy studies of $\rm Bi_2Sr_2CaCu_2O_x$.
