  We show that a localized bosonic mode acts as a new type of "defect" in s-
and d_{x^2-y^2}-wave superconductors. The mode induces bound or resonance
states, whose spectral signature are peaks in the superconductor's density of
states (DOS). We study the peaks' shape and energy as a function of temperature
and the mode's frequency and lifetime. We identify several characteristic
signatures of the localized mode that qualitatively distinguishes its effects
from those of magnetic or non-magnetic impurities.
