With the little I have to go on, I would say to take a look to the fuser, I've only seen it a few times (and on other machines) but you get an effect like that when the fuser roller/web assembly is defective and comes *unraveled* (That really isn't the right word)
I just noticed this issue from our Colorpress 800, almost looks like it has gotten wet but this was fresh off the stacker tray.. I have noticed it mostly on blacks and greys. Any ideas?