2007 Lincoln MKZ - Noise in low gears

What causes a winding/meshing noise from automatic transmission in lower gears?

Have you checked the fluid level and that it is not dark and burnt.

Yosemite

Yes, also, a fluid change of all but what is in the converter. No sign of any metal on plug when fluid was changed.

The sound is worse when cold, but still noticeable after warming up. Odometer turned over 100K a few days ago.