Please eliminate any possible natural explanation for what you are experiencing.
Could the sound be caused by an animal? Is there any way an animal could have gotten into the house? Remember, mice, squirrels, and even cats frequently get into homes through very small spaces. They can be responsible for small objects going missing, scratching sounds in the walls, floor, or ceilings, and even voice-like sounds, especially crying!
The wind has been known to make very eerie sounds, very similar to voices. Check windows and doors. Cold spots can be caused by a very slight gap in insulation or between window and door frames. This can also be the cause of doors opening and closing, or even rocking chairs rocking! If an animal has been eliminated as the source of a scratching noise, please check the landscaping. Is there a nearby tree or shrub that could be causing the scratching sounds? Also, An underground stream or fault line might produce strange noises. The same goes for abandoned mine shafts. The presence of these can be investigated through examination of topographical maps of the area.
Leaking pipes can cause noises like groaning and moaning , or even like voices as well! Check the pipes to see if sounds can possibly be attributed to this.
Yes, people! Have the phenomena been experienced by more than one person? Is there independent corroboration? Make sure that the phenomena cannot be attributed to a vivid imagination or any kind of medical condition of the witness. Drugs, alcohol, even reactions to medication as well as some mental or medical disorders may cause people to experience forgetfulness and hallucinations that may be visual or audible!
If there is no apparent natural explanation, then yes, you may have a ghost! Ghosts manifest in different ways at different times to different people. There are even different kinds of ghosts: the intelligent haunting and the residual haunting. An intelligent haunting responds to and/or interacts with the living. A residual haunting does not and is not, as far as we know , even aware of the living, but is similar to a movie being played over and over again.
A ghost may manifest in any way that may be experienced through any of the human senses alone or any combination of these. It may be a very subtle passing scent(smell) or may appear as a solid person(sight). It may speak or whisper, or sob(sound). The sounds may be intelligible or muffled(sound). The ghost may appear as a shadow or as a light of any shape or size(sight). It may manifest as a simple cold or hot spot(touch).
Remember that most haunting are, essentially, a person without a body. Whatever attitude this person had in life, they will have in death. Deal with them as you would deal with any person. Try to understand them, and help them work throughw hatever is keeping them here. They may have unfinished business, they may be afraid of the afterlife, or maybe they just want someone to listen to what they have to say before moving on. Just like people, ghosts may have abandonment issues, self-esteem problems, mental illnesses,loneliness,regret, and anger to resolve.
I have read of, but never actually experienced or witnessed hauntings that can't be resolved by a gentle, listening approach. these are spirits that have so much rage, or are so mentally disturbed that they manifest through physical violence against people and/or property. Perhaps this can be attributed to a spirit that in life has retained a psychosis and continues to have psychotic rages. Also, a sociopath would retain these feelings after death, and would have the same rage and hostility after death as they did in life - mayb even more so.
Try to find out the history of the house. Was there a murder or suicide there? Was there a grave injustice or tragic romance? Did violence aoccur at the house or on the property? What was there before the present structure? Also, please rememebr that teenagers may attract or generate psychic energy that may manifest as a poltergeist type haunting.