75 yr old mom hearing voices.

Auditory hallucinations can occur for many reasons, one of them being hearing impairment. Get mom to an ENT doctor for a hearing test asap, that's my suggestion.

Here is a link to a good article talking about the various possible
reasons for hearing voices:

https://my.clevelandclinic.org/health/symptoms/23233-auditory-hallucinations

Best of luck to you.

Your mom may need a more thorough memory testing(the 3 hour one)than the short simple one that most doctors office use, as it sounds like she may have some dementia going on.
Her doctor or neurologist can get that scheduled for her.

In your profile you say your mother is home with age related issues and with Alzheimers dementia.
Here you say that your mother passed all cognitive tests.
Yet she is hallucinating.
I am assuming that you have seen a GOOD neuro-psyc consult. If not, you should.
You should also ask if she has been checked out for anything like Lewy's dementia or Parkinsons. Both have hallucination as a side effect and both are easily missed in early stages.

That done--all of the above--it is time to have a psychiatric exam that concentrates on mental illness or mental disorders. It is now recognized that almost 25% of people with bipolar disorder are being diagnosed after age 60. Sadly, the wife of my partner's best friend was just diagnosed with LOBP or late onset bipolar.

Good luck, but this is a problem for the medical diagnostics team, and followup until answers are found is the requirement. I am sorry you are going through this.

Recent change of medication?
Not dehydrated or constipated? No pain anywhere?

How is her sleep? Any recent changes there?

No one-sided weakness (even subtle)? Stroke ruled out?

Shortly before my mom died, she saw a little girl.

She told me about conversations that she had with this child. Mom was comforted by her. So, I went along with it.

Is your mom frightened by these voices? Is she seeing people too?

I would say to make an appointment with a neurologist and explain her symptoms. Bring a list of all meds that your mom is taking.

Wishing you and your mother all the best.

Has she seen a neurologist? I’d start there

i hear from my dad's psychiatrist that hallucinations can go along with dementia. I think she needs to see a neurologist or psychiatrist to evaluate