My printer sits on a wood table, and while the printer is fairly silent, the vibrations resonate in the table which causes a lot of noise. I was reading about passive isolation of vibration on Wikipedia and kicking myself for recently having thrown away two old Ikea cork pot stands, when I saw an empty cardboard box that I hadn’t thrown out yet. I sliced it into four suitable strips, folded them each once, and placed one under each foot. This actually worked better than some rubber dampers I bought in a hardware store. 
Old mouse pads work well, too.
Or you could bolt the printer down to the table. that’s what I did with mine. Didn’t like it wobbling around, possibly off the edge of the table.
@Tom_Oyvind_Hogstad , yep, that’s the page I was reading. 
I guess you don’t need it though. your reprap is very quiet!
Can always be quieter. Interesting article. Will experiment a little with cardboard
Lin Engineering or Astrosyn stepper motor isolation mounts work wonders. Something else folks swear by is sorbothane bumbers (not rubber or mouse pads or cardboard). I already had silicone feet but the motor mounts had an amazing quieting effect.