How about you just don't listen to those sounds? Even in small apartments the bathroom tends to be separated from the living room/kitchen/bedroom/etc_room so it tends to be quite easy to ignore those sounds by just not hanging around the bathroom door.

Nope, this is taking social sensitivity far too far. By all means keep those farts out of polite company but once you're in the loo feel free to let it fly without feeling ashamed. Everyone farts, everyone pees, everyone does it.