Locate the leveling screw above the base wheel on your EZ-8 drum sander. Turn the screw clockwise to level the sander on the drive belt side of the drum or counterclockwise to sand more on the side across from the drive belts. Leveling the sander should help reduce or eliminate chatter marks.
Examine the wheels for any debris that may be contributing to the problem and wipe the wheels clean with a clean, damp cloth then dry them off.
Remove the wheels on the floor sander with a Phillips head screwdriver if they are deformed or otherwise damaged. Replace them with new caster wheels, available through the manufacturer or from many hardware stores.
Reduce the sandpaper grain size until the chatter marks are resolved. Use 36- or 40-grit sandpaper until the chatter marks no longer occur.
Move the sander in the direction of the grain and maintain an even, steady pace for best results.