Lately, my 85 yr. old wife with AD is spooked and jumps when I make a noise or speak and she doesn't know I'm there.

You will have to adapt your approach as well as you can, approaching always from in front of her. Startle reflexes are very common as is noise intolerance and startle reflex in response. So sorry you are going through this. Wish I had better advice. Do a bit of research online and discuss with her MD next visit.

Here is a link to a useful article by dementia expert Teepa Snow about why a person living with later stage dementia startles so easily:

https://teepasnow.com/blog/why-a-person-living-with-later-stage-dementia-startles-so-easily/

I have a heightened startle reflex myself (Not due to AD/dementia) and use earplugs which I find helpful to reduce noise pollution in general. Xanax helps as well as Paxil which I took years ago for an extended period of time. Speak to your wife's doctor about which meds may help her best.

It sounds like she is extremely anxious. Even people without Alzheimer’s disease tend to become startled by normal things when they are overwhelmed or stressed out.

Is your wife on any calming medication?

My mom had dementia with her Parkinson’s disease. She was prescribed Ativan and Seroquel. I saw a big difference in her ability to calm down after taking meds.

Best wishes to you and your wife.