I would start by swapping the tray cassette from the tray 3 position in the problem machine to the tray 2 position, or with a tray in the other working machine. If it follows the tray, you may have a failure with the tray it's self, such as a broken lift gear or paper lift plate.
However if you continue to have the issue in the same position on the problem machine, you may have an issue with part of the feed mechanism in the tray 3 housing, which is all one complete unit. If the machine has a warranty or contract I would advise contacting support and they can ship you a replacement tray assembly.
Recently, there have been a large number of "jams" on the primary machine which require tray 3 to be removed. As soon as it's removed, whatever paper was stuck moves through the system and printing continues. The next sheet of paper, in the tray itself, always has a deformation close to the top where the rubber roller would have tried to feed it through. I do not know if the two are related. It's jamming out of tray three about once every 10 or 15 pages.
Does anyone know what needs to be done in this case?