When I printed my "underground newspaper" on a dot matrix printer, back in high school, I thought I'd get away with so much printing without my dad knowing by putting a cardboard box over the printer to deaden the sound. It worked until it didn't. Luckily the printer had a thermistor on the printhead and just stopped versus continuing to brainlessly grind until seizing-up.
We didn't keep at it long, but that kept the noise from being an issue. It was a slow, messy process and we were too busy to pay attention to it over long periods of time.