Is there a sound?
I heard that some people (the ones on life support) make sounds.
What does it feel like emotionally?
Part of me always wonders, what if the doctors are wrong
and this person has a chance?
Not sure what you're asking exactly. Part of my job requires me to be the one to 'pull the plug', although that's not exactly the right description. A person on a ventilator shouldn't be able to make any sound, however, sometimes the cuff around the endotracheal tube that seals the airway, leaks. Or it blows entirely. When that happens, the patient can make sounds because air can flow across the vocal cords. Most of the time, no, a patient can not speak or moan when they are on a ventilator. The breathing tube passes between the cords, and the cuff seals it, so the only air goes down the tube directly to the lungs, and returns the same way. It's a closed system.
When we pull the tube, the patient may gasp, cough, gag, etc. After a minute or so, they can speak, although they'll probably have a sore throat. The machine itself may beep, if the respiratory therapist didn't hit the silence alarm. It's not a big deal though, since they are pulling the tube anyway. Sometimes I'm on the other side of the bed from the vent because it's easier to reach the patient or whatever.
Actually pulling the plug of the vent is no different than unplugging a toaster. It's the ET tube that matters. Also, not everyone dies immediately. Sometimes it's fairly quick, but I've seen them hang on a day or so.
ETA: Not everyone who is taken off the vent is brain dead (when we are pulling the plug--most of the time, we take them off because they are getting better). Some patients come into the ER, are then resuscitated and placed on a vent before it's found out that they wanted to be a DNR. The family comes in and says, "No, he doesn't want this." and the patient can even be awake by this time. (I can think of three cases in the last month, actually) Their disease process is such that the chance of them ever coming off the vent and being well, is so tiny, that they don't want to go through all that only to have the same end result. Often, family will want a little time to gather at the bedside, and the vent will buy them some time. We don't do any of this without the doctors and nurses making sure this is what the patient wanted. Like I said, sometimes the patient can even make the decision if they are alert enough.