A little question

I have noticed that the KH director only pops once at the beginning of the test then I don't hear it it again where I think I remember hearing it popping throughout the test, not sure if there's an issue but it does click so I know the pinch valve works but not sure if something has changed? is there anything I can check? I opened it up and looked at the valve and it opens ok but strange it doesn't seem to click through the test? will this make a difference to the test result or is it not a big deal?

Regards Adam