I seem to have much the same issue on my px-s1000. I have just had my keyboard for about a month , but been playing more than an hour a day. The black keys I use the most are starting to make a clicking sound. But I also noticed if you are pushing the black keys slightly from the right side, you can hear a click. From the left side,
VID_20200627_144541.mp4
it is normally not possible to notice.