My mom, who is 86 years old, started humming all the time. It's the same couple of notes over and over again. She'll do it pretty much whenever she's not eating or talking. I noticed it began after she had knee replacement surgery, and I fear she may have had a mini stroke as she came out of anesthesia. Nothing was ever mentioned by her doctor or surgeon about this, but it was a long time before she was brought back to her room, and as I waited in the room for her I heard a code red called. I asked staff about this, and they acted rather strange but said nothing. Other than that, she remains cognitively the same, and no signs of Alzheimer's. It's been a couple of years, and I'm just curious what causes this, and if it is a sign of something worse.