Same with doing cliff winching in an updraft in the Sea King Syd - no chance of reading any instruments at all.
However the inflow angle changes at the rear as well with the front seeing a bigger change than the rear, hence the dissymmetry.
Normally the vibration is associated with translational lift rather than inflow roll.
In a still air transition the inflow roll happens first, then the flapback and then, when you overcome both, the vibration of ETL.
I thought the vibration was due to the uneven forces across the disc, when inflow roll was at its worst. That period in slow acceleration when only part of the disc has moved out the induced flow. What would be causing a vibration at ETL?