If it sounds like a crunching, then your budgie is grinding his little beak and he is content.
If it sounds more like an intermittent clicking, (I liken it to 'clucking'
) then he's likely also content but the mechanism is different in that the noise comes from the throat rather than the beak. Think of it like a cat purring, but this is more of a clicky-sounding chirp.
Now one thing we have to be aware of is any clicking that corresponds to the breathing. If on each breath, a budgie clicks, squeaks or makes any other sort of noise, then it could be the beginnings of a respiratory infection and an avian vet visit would be in order. I'm only mentioning this so that members do not potentially interpret all clicking noises as being normal, not that I think anything is wrong with your budgie.