Minor vibration changes can be difficult to pick up for many pilots, including me.
If the change is slow, and over a long period, even more so.
It’s “thread drift” here though. Vibes/tapping were reported by one pilot, confirmed by another. An out of balance TR was then eliminated as a source.
The RFM call’s for a low hover, followed by a shut down and re-inspection. (Assuming the Vibe was no longer present in the low hover)
Rather than the above procedure, the report seems to indicate, that pax were loaded for what was essentially a maintenance test flight.
Am I missing something?