Epson 3800 rear feed clunking (head impact)

I have an Epson 3800 that has developed a problem. When I use the rear sheet feeder, as the paper feeds and prints occur, I head clunking when the print head moves. I notice that when running a nozzle check, the black and light black sections are not straight - they’re wavy. I suspect that the rear feed mechanism is causing something to stick up a bit, resulting in the paper being warped enough to both cause the wavy lines and the head is striking the paper.

Has anyone else seen this, and figured out what needs to be done to fix it?