Backlash type feel on rear hub?

In trying to identify which, if either, of my rear hubs is making noise, I jacked the back end up one side at a time and made the following observations:

No noise when spinning by hand (not surprising since the noise doesn't start until ~20 mph).

No roughness or play either.

A tight spot on the driver side but that feels like disc runout contacting the pads

When spinning either wheel forwards and back (just a few inches) there is a tap/knock on changing direction like you get when it is on a drive wheel, with the backlash in the drivetrain, but not as obvious. Should there be anything like this? The stub axle is solid and hub assembly is solid, i.e the only moving part should be between the inner and outer bearing shells, so it is like there is backlash in the bearing?