Dark Lord: So, tell, me DemandredÖ.Damn, my ampÖitís lost power.
Demandred: Iíll plug it back in, Great Lord. HOW ABOUT NOW. HEY, NOW IíVE GOT THE BIG VOICE.
Dark Lord: Stop that.
Demandred: SORRY, GREAT LORD, BUT I DONíT KNOW HOW TO TURN OFF MY OWN BIG VOICE. HEY. THIS IS KIND OF COOL. I AM THE GREAT LORD. OBEY ME OR DIE. LET THE LORD OF CHAOS RULE.
Harry Potter has a lot of difficulty keeping his voice at a normal volume in Harry Potter and the Order of the Phoenix. Even when he's not in CAPSLOCK!Harry mode, you can make a drinking game out of the number of times Ron or Hermione indicate that he's getting unnecessarily loud for the situation. Semi-justified in that Harry appears to be suffering from a mild form of PTSD (and most likely puberty) and gets frustrated a lot.
Gullivers Travels: Gulliver has to develop this when he was in Brobdingnag in order for the sixty-foot tall inhabitants to even hear him. Naturally, when he got back to England he was still yelling out of habit.
In the The Phantom Tollbooth, Dr. Kakofonous A. Dischord, Doctor of Dissonance, whose middle name is AS LOUD AS POSSIBLE!
Despite not having what we would call a "voice", Visser Three fits this trope to a "T". He seems to have no concept of private thought-speak, and constantly broadcasts everything he says to everyone in range.
Similarly, Jake describes Crayak's "voice" as Crayak screaming at the top of his lungs.
Mr. Men: Mr. Noisy and Little Miss Loud fit this trope to a "T".
In the Jeeves and Wooster stories and novels, a lifetime of fox-hunt halloos has left Bertie's Aunt Dahlia with this sort of voice.
In Men at Arms, one of the recruits for the City Watch is the town crier. His speech is all represented in Caps Lock.
Colon: And who are you?
Silas Cumberbatch: SILAS! CUMBERBATCH!
Colon: Didn't you used to be town crier?
Silas: THAT'S RIGHT!
Mr. Howell, the strict teacher in the Origami Yoda series, has this. Being a strict teacher, he loudly yells at students who misbehave, and even those who don't misbehave.
Ivy Carson in Zilpha Keatley Snyder's The Changeling is described as having a loud, clear voice. When Martha first hears her, she expects the teacher to say something to her about using a "good classroom voice."