Without a more concise description of "violent vibration" (direction, periodicity, intensity, any other qualities, etc), I can only make some guesses:
It could be a position sensor, like a motor hall sensor, that is either not signalling correctly (bad sensor or magnet fault) or is not able to send it's signal to the controller (broken or intermittent connection anywhere between sensor and cotnroller PCB inside it's casing).
It could be a battery or BMS problem, where voltage drops on a cell or a sense wire causing the BMS to cut power, then the voltage rises, then the BMS turns back on, then voltage drops again, then the BMS cuts power, etc.
It could be a mechanical issue, like a bearing, causing drag or actually broken so it catches, releases, catches, releases.
Or if it's a planetary gear reduction on the motor, it could have broken teeth on one or more gears, etc.
If you can provide significantly more detail on the problem, what led up to it, how it developed over time, and how the system itself worked when it was normally operating, it may help us help you figure it out.