The Freelings were haunted by the ghost of Tweety.
- Nothing weird ever happened in that house until the canary died. Tweety came back for revenge.
- But Tweety's then targeting Carol Anne, the only one who wanted to give him/her a proper burial, instead of Diane, who wanted to unceremoniously flush him/her through the toilet, or Dana, who scoffed at Carol Anne giving him/her a proper burial. What a dick of a bird!
Tweety's death (indirectly) was what triggered the Poltergeist manifestations
- Tweety was not a ghost or haunting the family himself, but his death indirectly set off the hauntings because he got a proper burial on the Freelings' ground. The spirits up until that point had just been lost/lonely/sad, but seeing a deceased creature getting a loving burial on their ground while their own graves and human remains had been violated on that ground, was what made them flip and that's why hell broke loose then. That also neatly answers the often-asked question of "If the Freelings have been living on that ground for >6 years, why do the "ghosts" manifest just now?".