The house that Jon Lord refers to is Deeves Hall in Hertfordshire. According to Jerry Bloom's book "Black Knight - The Ritchie Blackmore Story" Lord and Nick were sharing a room and experience a few weird things, such as tappings on the window and creaking floorboards. The building was reputedly haunted, although how much of it was down to Ritchie's penchant for practical jokes is open to question!