  We propose a new source for the cosmological density perturbation which is
passive fluctuations of the inflaton driven dynamically by a colored quantum
noise as a result of its coupling to other massive quantum fields. The created
fluctuations grow with time during inflation before horizon-crossing. However,
the larger-scale modes cross out the horizon earlier, thus resulting in a
suppression of their density perturbation as compared with those on small
scales. By using current observed CMB data to constrain the parameters
introudced, we find that a significant contribution from the noise-driven
perturbation to the density perturbation is still allowed. It in turn gives
rise to a suppression of the large-scale CMB anisotropy that may be relevant to
the observed low quadrupole in the WMAP CMB anisotropy data. We also briefly
discuss the implications to the energy scale of inflation and the spectral
index and non-Gaussianity of the density perturbation.
