Are you talking about a bump streak that repeats water pickup from a hard edge at the gripper?
Some remedies for this are:
Ensure proper roller settings, especially in dampening unit
Make sure pressures between plate/blanket are correct
Feather blanket packing so that image transfer is a little more graduated
Use imposition software to break the hard edge with something curved or squiggly at the gripper, out of image area
Use imposition software to slightly rotate the solid (if possible, i know this can't be done on form work) in order to break the hard edge
Move ink charge/oscillation
Oscillate form rollers
Change press speed
I'm sure there are more ways to troubleshoot this problem but these have always worked well for me and other pressman I've been around. Making adjustments to the imposition seems to be the most effective and least time-consuming. Sometimes you can only make the streaks better but not go away entirely. Mechanical defects can also cause this (sloppy gears, press not being level on floor, etc.)
Hope that helps.
