There is a chance that is related to the pump motor and the wiper. From time to time you can get a build up of ink around the wiper blade and down which can cause the wiper to stick and not move. Or the gears for the pump are catching somewhere and not turning. If you have the front open to watch this area you will notice that the gears are not turning when this noise happens. On the older Rolands you can move the wiper by hand and if its stuck, release it.
If the gears are wearing it could be a spot in the gears that if the pump happens to stop there then that noise may happen next time it goes to clean or on startup.
If you thought you could remove the pump and clean that area out that may help.