Improvised suppressors do not work on the Izh 18 rifle in the sense that zombies can still hear the gun shot as though it was normal with them running to the gun shot from quite some distance from my brief test.

Cannot tell whether other people can hear the shot as though no suppressor is on the rifle but the person with the rifle can hear the audio of the gunshot as though it was using the improvised suppressor so I cannot put it into the more accurate category, sorry.