The 1st video has accelerometer mounted on a thin flange of a cover. It would be good to check mounting location by moving to the engine case/block.
If the signal is real and causing accelerometer overloads, then check for dominant frequency in spectrum and view the acceleration-time waveform for impact events.
If vessel has two D-G, then make comparison measurements including on the auxiliary components (water and oil pumps). Any other signs of poor condition such as cylinder pressures and temperatures and lube oil flow and temperatures?