My mother has had dementia for about 10 years now. She is starting to hear things. Have you experienced this? I just agree with her.

You are doing the right thing by NOT ARGUING. Arguing doesn't help at all..
it doesn't hurt to get UTI checked. That may be a reason for this issue too as 97yearold replied

Also be sure to get her tested for a UTI when possible. This is sometimes the cause of hallucinations.

Hallucinations are quite common with dementia. Hallucinations are sensory issues... seeing, hearing, feeling things that are not there. These are not imaginary issues to the person, they are real. Your agreeing with her is precisely what you should do. Validate her reality, it is different than yours. We naturally try to correct someone's belief if it is irrational. To some one with dementia, these "irrational" beliefs are true. Trying to correct them will only result in conflict. So continue trying to be part of her reality.

You might want to read "Learning to Speak Alzheimer's". It's a great book for caregivers. Good luck.