Is this a new to you printer? Or have you had it for a while and it just started doing this?
If you just picked it up it might be things are not alligned propper. One head may be out of allignment. You can do print tests in the service manual that will show if the heads are lined up propper.
If its trying to mix a color from your left head (Black,Cyan,Magenta) with the right head (which has yellow, LT cyan and Lt Magenta) and its way out of allignment, this may cause a band of yellow to show around the image on things that need a yellow mix and not show as much with the Lt Cyan and Lt Magenta.
If you can get a photo uploaded it would be better to see what you have happening. If the above is true you should also see a thin line on the opposite side (offset) where the yellow has not mixed.