Generally when we see problems like this, it's due to the printer accepting *any* input to its listener, and dutifully printing that out.
I'd start by taking a printer, looking at the open ports, and scanning those ports one at a time, isolating the problem to a particular port/service. Once that's done, you can either telnet to the port, send it some garbage, and see if it prints, or you can call our support team to have them walk you through a debug scan.
With the debug scan, we can tell you exactly what we're sending to the port. We *may* be able to mitigate this, but you'll likely have to end up contacting the vendor, as ultimately they're the ones who'll have to get their printers to stop blindly accepting input without any semblance of validation.
Hope this helps,
You can often do this from your desktop. Telnet to port 9100 on the printer, start typing and hitting enter, often it causes the same behavior.
I have seen this at Universities I have worked with. They did exactly as Chris describes above by isolating the port. Sometimes there are firmware upgrades that will stop the behavior.