I have a stock y21 transmission

when I have the car up on jackstands and the wheels off, I can crab the axle right where it goes into the tranny and twist it back and forth about 1/4inch (just taking up the slop /lash). I know that's pretty normal, but there's an audible "clank" as I twist back and forth.

I can hear the clank plainly when driving too (especially in lower gears) when I jam on or let off the gas (loading up the driveline one way or another).

Are these signs that the differential is going bad? Are there other symptoms to check for?

thanks