1/2 quart low in rear differential on my 2018 TRD Pro

What weight is the factory fill?

 

My diff has a slight howl. Wonder if I need to have it checked.

 

tranny fluid has to be checked at a certain temperature,,

 

For those getting the idea that low fluid has anything to do with the rear diff howl, this has been discussed at length in more than a few threads. No direct correlation.
Mine howls, still has the factory fluid, and has been properly filled from day one. The TSB for this "NVH" issue details a solution that basically reduces the effect with updated cab mounts/rear leaf packs/sound deadening material in the rear corners of the cab. It's obvious that Toyota is attempting to stop (or at least attenuate) the vibrations coming from the diff from transmitting to the rest of the truck.

Having said this, I'm sure there are outliers who have changed their fluid for another product and are happy with the results.