i'll have to give it a try. i knew i had read somewhere that people could do it with a diaphragm but i'd never seen anyone explain it.

Rd, i make gobbles on tube calls by saying "Tuk-tuka-tuka-tuka"

the first "tuk" is a louder one note sound, and the tuka tuka tuka is done rapidly. it is hard to explain but keep playing around with it and you'll get it.