Enstrom
Hallo IV Flyer ... as an experienced Enstrom pilot and FI, I have to endorse the last two posts. Please have a type experienced engineer go through the drive system as from the two videos you have posted, the level of cabin vibration is excessive. If you do not know, the rotor blade tracking with Vibrex tracking equipment or similar should bring the accelerations to UNDER .1 (being one tenth of an inch per second.) I'm sure your engineer will know all this. Suspect components can be Lamiflex bearings, dampers, excessive friction in the control system or possibly just poor RB tracking.
Enjoy your Enstrom. DRK