Keith
I had this happen on my R2400. It drove me crazy trying to track down the problem, but it turned out to be a piece of fluff or cat hair perhaps stuck to the print head. Since then I have always kept a cover on the printer when not in use.
Oh, of course, it might be helpful to know how I fixed it. This may not help, because the 2400 and 3880 are obviously somewhat different, but anyhow -
* I could find no way of getting at the print head on the R2400. So I powered the printer up, and as soon as the print head moved to the left I switched off at the power socket (not the printer). This leaves the print head unlocked and free to move along the carriage.
* On the left on the 2400 are two foam pads just off the platen. I carefully removed these, cleaned them, replaced them and then soaked them in a mixture of water, alchohol and detergent (screen-wash fluid, actually).
* I then parked the print head over the platen pads and left it there for an hour or so.
* Then I fired up the printer and printed some areas of solid tone, of black and each colour. The paper came out covered in all sorts of junk - little hairs, fluff , you name it. About three year's worth of crap.
Since then it has been brilliant. Not a blob or streak.
Of course the other thing you can do is make sure that the cats are never let into your studio . . .
John