I've tracked a quiet knocking noise to my passenger side inner CV joint. The axle has a very small amount of rotational play within the CV cup, and it sounds like the bearings are able to move a bit, to slap against the cup surface when you twist the axle back and forth. I only noticed the sound because I had the car on stands and was running it in first gear (zero load against the wheels) to move all the fluids around during an extended storage period. As the wheels turned with the engine, I could hear a subtle knocking sound from the rear end, and was able to track it to the CV cup. With the car off, I can recreate the sound by grabbing the axle and rotating it back and forth.

I do not have the dreaded "axle click" from the hub, or any vibration while accelerating. These are used OEM axles with CV cups swapped left/right. The car is lowered for track use. I've put 30,000 miles on these axles with this setup. The grease in the cups is Amsoil heavy duty grease.

Anything to worry about, or just the normal result of the cups wearing and creating gradually larger tolerances against their bearings?

 

The play in the axle cup is normal.

 

With the car on stands, there is no load. So the wheels are going to unnaturally rock forward and back, banging against any play.

On the road, there is always load which pushes the play solidly in one direction. Even when cruising a constant speed there is mechanical load, aero load, rolling resistance load.

 

A reply from Billman is a reply from the S2000 god himself! I will sleep easier.

Thanks guys!