Indeed, check oleos, check tire pressure, check main rotor dampers.
Do you park it outside overnight? Temperature differences have effect on the dampers as well. Usually a 10 minute ground run should bring everything to an operational condition.
If this does not work, our engineers turn to the log cards and start comparing balancing mass and pitch rod settings with the current conditions. (Sometimes the trim tabs, however, considering your situation these can be ruled out - i.e. fast forward flight only).
Please let us know if the situation has resolved and what action led to a possible solution. Good luck!