It happened again now. It only happens at night when I’m the only one still up. Sometimes when I go to the kitchen to make myself some coffee I hear the voices of my parents murmuring stuff. Then I go check out and they are still in bed sleeping
Should I be worried about it? I am going to talk about that to my psychologist. I use Prozac, I drink and smoke sometimes and have never done an illegal drug.
…advices?
Definitely tell your shrink about it. It’s one possible sign of schizophrenia.
You should get yourself checked out in case it’s a symptom of something else. It could be harmless (benign hallucinations aren’t all that rare actually), it could be a symptom of all sorts of problems.
You might mention it to your medical doctor as well. Hearing indecipherable sounds might have a physical component. I’m thinking maybe some kind of odd neuro symptom? Or tinnitus?
I wonder, since it only happens at night when you are the only one up, whether you are hearing normal house sounds (water in pipes, furnace, fan) and interpreting them as voices. That happens to me and I’m not schizophrenic. It’s always some barely-there song or radio announcer under the white noise.
Is it possible one of your parents talks in their sleep? Your going to their room may disrupt the process so it is quiet when you look. Neighbour sounds seeping in? I am not sure that hearing vague murmerings is quite the same thing as what is usually considered “hearing voices” however, psychologists are there to talk to about stuff that is bothering you and this is, so do talk about it but don’t start with the phrase “hearing voices” because that particular phrase sets off bells you may not need rung and if you do it will come out in time anyway. Hearing things late at night that you can’t explain may be a better beginning.
This page makes sense to me on the subject as someone who lives with the experience http://www.mentalhealth.org.uk/help-information/mental-health-a-z/H/hearing-voices/
Def talk to doctor. But don’t stress over it in the meantime. Hallucinations like that are more common than often thought. It could be like a previous poster mentioned, sleep talking, noises in the house that your brain is trying to make sense of, or a sleep disturbance where you are half sleep.
It could also be associated with stress, migraines, unusual seizures, a medication you are taking, tinnitus, or schizophrenia.
I am not a doctor.
I am glad you intend to address this with your doctor.
But don’t scare yourself over these experiences. You should be screened for the serious stuff just in case, but statistically it is not serious. And there are treatments for many of these things. (I have a lot of non-medical contract with populations who have high incidents of interesting medical and psychological conditions.)
Is it actual voices or quiet sounds that could maybe sound like super low talking or mumbling?
It’s common to hear all these quiet sounds at night, because the sounds that drown them out during the day are gone. Humans are basically hard-wired to detect patterns from ANYTHING (images, sounds, famous deaths happening in 3s, etc), even though there’s no actual pattern there.
On top of that, auditory hallucinations can result from heavy caffeine consumption or lack of sleep. Often these can go hand in hand (needing caffeine to stay up, etc) AND can result in you being awake late at night, so you’d hit the trifecta, there. 
Being in grad school, I’ve had that combo quite often, especially since my best hours to really focus and be productive are ~1am-5am. I’ve had many nights where I’d finally go to bed to get a couple hours of sleep and I would hear what sounded like the quiet, muffled audio from a tv or radio playing in the flat below us. I knew it wasn’t real because I know they’re asleep by then and it sounded like a 1950s-style evening talk show/variety hour with the brass-heavy musical accompaniment. But I swear to god, I was HEARING it, I really was, while simultaneously knowing it was a hallucination. Quite jarring, lemme tell ya.
tl;dr - yeah, hearing voices CAN be serious (like schizophrenia), BUT its far more likely to be no big deal, other than perhaps a sign to cut down your caffeine or get more sleep.
OP’s described symptoms are so mild, and so generally similar to other peoples’ experiences (e.g., Silvorange and zweisamkeit above), that it doesn’t sound like anything that should even be mentioned to any doctor, unless it becomes more pronounced than this.
On the other hand, if you do mention it to a doctor or psychiatrist, you are very likely to be “diagnosed” with some kind of mental illness, possibly with adverse effects to you, that are more appropriate for someone more seriously ill. You might find your medical insurance premium jacked up sky-high or you might become uninsurable. As a more extreme possibility, your doctor might find it necessary under the law to report you to your state’s motor vehicle department, which might cancel your driver’s license. (I don’t know if they really do that to mentally ill people. The point is, there might be no distinction made between a trivially minor perceived malady versus a severe debilitating version of the same. )
(Missed edit window)
ETA:
A more severe possibility is that you will be committed to a mental hospital for a 48-hour or 72-hour “observation” period, during which you will be “evaluated”. Mental hospitals are notorious for never (well, hardly ever) evaluating anyone as not having a mental problem. Just like many jurors in trials allegedly think “if the defendant is on trial here, he must be guilty”, it sometimes seems like mental health professionals think “if the patient is in the hospital here, he must have a mental problem”.
This was investigated by David Rosenhan in the infamous Pseudo-Patient Experiment, published to much controversy in 1973, in which actors gained admittance to mental hospitals for evaluation and then proceeded to behave completely normally. Typically, the hospitals never recognized them to be “normal”.
ETA: Link to Rosenhan’s paper, On Being Sane in Insane Places.
Senegoid:
Yellow Kazooie is in Brazil, which provides universal, free healthcare to its citizens, so your concerns about possible consequences for his insurance are misplaced. Although the symptoms he describes may be of no significance, they also could well be early signs of incipient schizophrenia or of some neurological problem. Even if they are caused by normal nighttime noises, the fact that he spontaneously interprets these as his parents’ voices is concerning. I agree with the majority of posters in this thread that he should talk to a doctor about these symptoms, and get tested if necessary. They could be early signs of serious diseases, that can be treated far more effectively if caught at an early stage than if left to develop into something more obvious. On the other hand, if, as is quite likely, they turn out to be harmless, nothing will have been lost.
Your (Senegoid) paranoid notions about psychiatry strike me as not very different from the delusions of anti-vaxers (or Scientologists, perhaps). There is always a very small chance, in any dealings with any branch of the medical profession, that one will be misdiagnosed and harmed by the treatment, and psychiatry is no exception in this regard, but I very much doubt your claims that psychiatrists are systematically inclined to diagnose problems where none exist. The dangers of not seeking medical advice for worrying symptoms far outweigh the danges of seeking it. If anything, the real problem for patents seeking mental health care when suffering relatively mild symptoms is the reverse of what you imply. Patient complaints about mild psychological symptoms are often too readily simply dismissed, or else treated perfunctorily with anti-depressants (which, I note, Yellow Kazooie is already on) in lieu of a more careful diagnosis or more appropriate but more expensive treatment. Anti-depressants are usually pretty harmless, but they also very often do not really do any good.
To imply to a person who may actually be showing early symptoms of serious mental illness (and certainly has genuine concerns that he may be), that if they mention their concerns to a doctor they are soon likely to find themselves involuntarily incarcerated in a lunatic asylum, even though they may be perfectly sane, strikes me as highly irresponsible. One Flew Over the Cuckoo’s Nest was not a documentary.
Thanks so much for all the replies. It was really nice of you. Especially zweisamkeit, because I like to believe that it was just because of lack of sleep and coffee overdose. I’ll see what I can do about that. I’m definately talking to my psychologist about that but I think I’ll wait more till I go to a doctor, if I ever will.
oh, @njtt, the free healthcare here in Brazil sucks, so I can’t count on it 
once again, thank you guys
Maybe so, but attempting to use it is not going to send your (non-existent) premiums through the roof, as Senegoid suggested (and as might really happen in America). Also, I am fairly confident that its suckiness arises mostly from under-funding, and thus consists much more in under-diagnosis and failure to provide adequate treatment where it is needed, rather than over-diagnosis and forcing people to undergo expensive unnecessary treatments.
I would mention it, particularly if it worries you, but not be overly concerned. It might be something serious, but it’s more likely not. Others have made the comment above that human brains are hell-bent on detecting patterns where there are none, and it may well be that your stressed brain is taking normal house noises and making them into something it thinks it ought to be paying attention to.
Anecdotally, I will also note that Prozac (fluoxetine) has many of the same side effects as anticholinergic antihistamines, as do many other SSRIs. Those antihistamines are the ones used in non-prescription sleeping pills in the US. It’s not uncommon for people using those for sleep to think they hear speech, particularly someone familiar calling their name, as they drift off. It just seems to be a quirk of that drug family.