could be a couple of things, and mind you I am not a jav owner
Our M&R does this when there is moisture in the line. Check that first. Second, make sure it's well oiled.
It could be whatever signals the press to move the squeegee back and forth. The MAC valves do this on an M&R. I imagine it's something similar on the jav.
Also, the seals in the stroke cylinder could be bad. How old is it? Oiling will help...temporarily. You can pop an air hose off and put a few drops of oil in and see if it helps.
