Ah Mike I made Rhencullen into two words, stupid me.
Some say that in olden times (Foster times) it went by the name of Renurling or Cronk Urleigh. But that was in the 1400s. There is talk that it was the place of assembly or Tynwald until 1428. Urleigh may come from the Irish urliadhe (place of slaughter) or eagle. However on todays course Cronk Urleigh is surely before Kirk Michael?
Other spellings are Rencullyn (Rencullin) A 1515 map shows Rhencullyn as a large area of land:
http://www.digiville.com/alexander/maps/farms.htm
Good name for a house though.