how to separate white guassian noise from signal in foureir domain

i have a signal with added white gaussian noise. i m doing some kind of mode decomposition. After mode decomposition the noise does not look random but have streaks like appearance in time domain. The mode decomposition is a wiener filter and it does linear decomposition. So it transforms the white noise as linear streaks. Please see the noise in frequency domain. The red is the signal and the output mode in blue has noise in it. I appreciate assistance

thanks
sal