Can you name that sound (squeaking)?

Grit dog wrote:
If it was the brakes, and it could be a harmless brake squeal, the noise would change or go away if you ride the brakes a little while maintaining speed. So not likely brakes.
If it’s not rpm sensitive then not likely to be the accessories or belt.
It’s not random, it’s rotational, so can likely rule out odd non moving parts squeaks as suggested it may be.
If I read your dash right, 111k miles. If it’s on original u joints or carrier bearing then those are the likely culprits. U joints can dry out and if very mild/shallow driveline angles (like a long RV) the u joints dont exercise much and can go a long time before actually showing other signs of pending failure.
After 100k miles u joints and carrier bearings are nearing the end of their service life, frequently.
But you have to get under it and diagnose. Any grease splatter or rusty dust around u joint cups is a sure diagnosis. Any slop in carrier bearing or torn rubber is as well.

Thanks for your suggestion. I continue to learn along the way...
I don't know much about u joints and carrier bearings. I did find this interesting article about u joints:
https://www.halesautomotive.com/news/shop-news/40-store-news/905-what-are-u-joints-and-how-can-you-diagnose-a-bad-one
I will try the test they suggest, and also look underneath the vehicle as you suggest. When driving, I do not feel clunking or jerkiness, so I'll be a little surprised if this is the issue.

I also had to look up Carrier Bearings... Here is what I found:

"Carrier Bearing—A carrier bearing is located on the axles or driveshaft and is integral to how the car operates. Its job is simply to keep the axle or driveshaft tightly in place and reduce vibrations. Worn carrier bearings can cause rumbling or whirling sounds for acceleration above twenty miles per hour."

Hmmmmm....the "whirling sounds for acceleration above twenty miles per hour" does describe my symptom. Also a good read:
https://www.driveshaftsoftulsa.com/blogs/news/symptoms-of-a-failing-support-bearing

I learned a lot about u-joints and carrier bearings when I found this video:
https://blog.1aauto.com/how-to-check-bad-carrier-bearings/

Now I know where/how to look. I'll have to investigate further.

Thanks!
Chris