The cyborg General Grievous was wheezy because he was trying to maintain the last remnants of his biological self in his mostly mechanical body. With the high level hi-tech cloning technology and the artificial limbs available in the medical field in Star Wars, I have to wonder why Darth Vader was dependent on his respiration suit in order to survive. I know he burned his lungs and that's why he wears the iconic self contained breathing suit. Is there a canon reason as to why they didn't just "fix him up"? Why was Darth Vader wheezy?
Vader's helmet was the center of the life-support system. It was fitted with an air pump, which was connected to a flat filter system worn on Vader's back. Together, the backpack and the air pump continuously cycled purified air through Vader's ravaged lungs. A small, back-up air-processing filter was located in his distinctive mouth grill, which also doubled as a respiratory intake system. Vader's life-support system also included a chest-worn, computerized control panel unit that regulated his respiratory functions. From this chest panel, a thick cable entered his torso, linking to a breathing apparatus and heartbeat regulator. The ventilator was implanted in his terribly scarred chest, along with tubes that ran directly into his damaged lungs, and others that entered his burned throat, so that should the chest plate or belt control panels develop a glitch, he could breathe unassisted air for a limited time out of his mouth, which had not been burned to the extent of his throat.
A belt-mounted function box housed the respiratory sensor matrix responsible for controlling Vader's breathing. Using it, Vader could easily adjust the controls on his armor to increase or decrease his supply of oxygen.
Vader's breathing was machine-regulated, but his pace of breathing quickened during physical exertion and could be overridden by involuntary emotional reactions. In addition, his respirator would also let out a strained rasp if undergoing extreme exertion rendering him exhausted or if part of his armor is significantly damaged. This is especially evident when Vader ended up having his right arm cut off by Luke Skywalker in their final duel. The respirator slowed down or sped up in response to changes in his remaining body's functions, but Vader was unable to stop it or hold his breath, nor could he slow it. Vader's breather functioned even while Vader was speaking.
However, it is apparent that a dampener or similar device had been installed into his suit by 3 ABY, as he was able to surprise Luke Skywalker in a dark passage near the carbon-freezing chamber on Bespin. Vader's ambush was only possible because he could temporarily quiet his loud breathing.
Lord Vader's breather was seriously damaged by Force lightning during his struggle with the Emperor. Although it continued to operate to some extent, the sound of the mechanism was reduced to a strained rasp, implying that the respirator was broken. The labored breathing sound persisted until his final unmasking.
His signature, labored mechanical breathing was the sound of the iron lung Vader was forced to wear. The med droids that had made the suit had inserted the redundant breathing tubes low enough so that, with the aid of an enunciator, his scorched vocal cords could still form sounds and words through a voice synthesizer in the mask. Absent from the enunciator in Vader's mouth grill, which imparted a synthetic bass tone, his own voice was little more than a whisper. Though limited by what the respirator could do, Vader could still make his respirator approximate a laugh or a sigh.
Because George Lucas said so:
...he falls into a volcanic pit and gets fried and is one destroyed being. That's why he has to wear the suit with a mask, because it's a breathing mask. It's like a walking iron lung.
What does an iron lung sound like?
Breathing inside a fully-concealed plastic suit would somehow affect the flow of sound he makes when he breathes, etc.