It's worth mentioning that if you over load a cap or it is excessively dirty (like getting goopy concentrates on it), it will not click as loud or you may get a delayed click. Try not to have material sticking out of your tip that can contact the bimetal discs.
Cap clicks definitely vary both from cap to cap and over time/with use in the same cap.
I have 6 caps and they all have different click volumes, but one of them is exceedingly quiet and has still become my favorite cap. I've learned to feel for the click-it's quite easy really once you know what to feel for. I believe that's called a haptic indicator. Just one more cool thing about vapcaps.