I've had the same problem for 20 years. I and my family have just accepted them. I think there is an emotional problem as they rarely happen when I'm in a meeting or in a public place. I'd love to know what causes them.
I have this exact same problem. I'm 19 and have had them this badly for at least 3 years, but know no cause or have found any solution yet.
My mother in law has had these exact same hiccups for over 7 years now. Every time she goes to a doctor about it, they always say they'd need to hear the hiccups for themselves and, of course, they don't come out when she's at the doctor. It is very loud, bird-like as you describe. It's pretty funny in a movie theater because everyone turns to see what the noise was and someone inevitably says "Bless you." haha. I am on the internet trying to find info about what it could be and haven't come across anything! Your post was over a year ago so you might never see this but please respond if you've found out any more information. Thank you!