Why does the gear shift knob of a Nissan sentra vibrates when speeding?
How bad is the vibrating? If you simply feel the vibrations when handling the knob but it doesn;t shake other times, it's just the machinery inside the transmission resonating throughout the shift linkage. If the knob simply moves without you feeling it, then you could have suspension problems in which vibrations are resonating up to the shift knob. Also, your shift linkage may be slightly loose.