^ here's some i synthesized this morning. mainly just simple waveforms run through delayed feedback to get a bit of unsynced wobble, and then the waveshaping patch i will attach to this mail.
my original thoughts about the wet filter didn't yield such good results, although that might have been because the one i made only has fairly short delay lines.
the farts i made a fairly crap ('scuse the pun), but kind of fart-like....however once i tried to lengthen the sound and play it melodically like in that track, it didn't work at all.
why not contact the author of that track and ask how they did it? 'excuse me, may i ask how you make your farts?" ..etc
i reckon they're probably samples, but a good synthesis method is also possible without a doubt.