I am not sure I can feel chatter apart from harshness and weepers, but I am convinced it is there when I have too little blade rigidity (especially with significant blade exposure), I get blade resonance driven by the stubble. The people I know with fine hair are not sensitive to it.
The way I can tell I am getting chatter is to put a shim under the cutting blade. If this smooths out the razor (even though there is increased gap and exposure due to the shim), I know it was the stiffening of the shim that helped by raising the natural frequency of the blade in the razor and avoiding resonance.
I also think if slowing the speed of the stroke helps a lot, it might point to chatter in that it indicates your initial harshness was due to the range of impact frequencies of stubble on blade initially extending to the natural frequency of the blade in the razor (and slowing down separates the frequencies eliminating blade rsonance).
Interestingly enough, I don't think completely rigid razors are as smooth as ones that allow some flexibility while still having enough rigidity to avoid chatter. The Futur noted above is one that has less than perfect rigidity while being smooth.