Two or three years ago I was bimbling along in the Luscombe minding my own business when a sudden vibration manifested itself. At the same time my pripheral vision picked up movement. The port lift strut had started to vibrate, somewhat alarming as it had never done so before. Something was clearly making it resonate. Judicius tweaking of throttle settings got rid of it and it did not subsequently return. Back on terra firma I phoned one of hte other group members to ask if it had ever happended to him.
"Was it raining?" he asked. Well, yes it was.
"Never had it happen to me, but I've read about it on one of the US Luscombe sites, it only happens when it is raining."
Weird