Originally Posted by Andrew R Stewart

There are many headsets with a split crown race seat. My understanding is that they are used to make up for less than best fork crown seat condition. One of the drawbacks to carbon fiber construction is not wanting to cut those fibers right at the focus of stress. So fitting a race seat ring that can expand as needed removes the need to machine a spec diameter, thus cutting the top layers of tow.

"Popping" noises from a headset area can have many causes. Dry contact surfaces and/or rough from corrosion/wear rolling elements are among the more common. With a cartridge bearing one can spin it while holding it in hand. But without real load the bearing doesn't always feel bad when it is in situ.

Do let us know what you've done to fix it. Andy