We show the importance of achieving an acceptable level of output side-mode-suppression ratio when generating pulses by using the self-seeded gain-switched technique. Experiments carried out on such pulses exhibiting poor side-mode-suppression ratios that are subsequently filtered to improve the latter demonstrate that they possess an associated level of noise. This buildup of noise with a decreasing inherent side-mode-suppression ratio is noted regardless of the improved output-filtered side-mode-suppression ratio of 35 dB that is maintained. The degradation of the signal is due to the mode partition effect and may render these pulses unsuitable for use in high-speed optical communications systems.