Lonewolf - yes I think a blade delamination or a faulty drag damper could easily cause the resonance - we had a situation in NI many years ago where a blade drag damper lock was left in and the aircraft started up. It was stable enough until flying Nr was reached and then it went pear-shaped very quickly - ISTR the crew got it airborne and then carried out a prompt running landing, shutting down the rotors as soon as the wheels touched the ground. Wessex pilots were very au fait with ground resonance issues.
I can imagine a crew, unfamiliar with the rapid onset of ground resonance, wanting to keep it on the deck as you don't know if it will get worse in the air - good idea but shut down the rotors immediately.
We used to demonstrate a damper check as part of the airtest qualification on the Sea King - you sat in the hover and circled the cyclic once or twice (fairly small circles but quickly) and then stopped to see how long it took for any oscillations to stop - a faulty drag damper was evidenced by a slow to reduce 1R.
It was possible to set up a sympathetic oscillation in the rotor which persisted as a 5R for a few seconds and was very unpleasant - a pilot who was trying to fault diagnose a damper issue managed exactly this and though he had lost control, dumped the lever and trashed a perfectly serviceable aircraft.