> The trouble began suddenly on the thirty-first of October 1998.
> The trouble began on the thirty-first of October 1998 suddenly.
sure, but natural isn't what a writer who is trying to persuade is going for. 'suddenly' in this example has a polarized value. as an adverb observation it inserts the writer into the story, which either has tremendous meaning, or literally none at all. I would even say that the second example has a more masculine voice than the first because the "trouble began suddenly" usage is careless, non-commital, and low risk.
A lot of what makes reading satisfying is pushing values onto the readers mental stack and popping them off in surprising ways, not unlike comedy setups or waiting for the drop. while I can be a bit turgid, I would have written this as:
"The trouble began on the thirty-first of October 1998, suddenly."
Adding the comma gives you suspense to resolve by popping it off with an example of suddenness. e.g.
"The doctors said it was a possible side effect of the seizure medication, but it was as though a resevoir of something stable and forgotten had breached. Victims in collisions with head injuries often have behavioural changes, they said, but he was not a victim, or even a perpetrator. what is the opposite, a protagonist? 'shopping cart jousting' was the line in his file adjacent to a generic billing code reserved for cases of decidedly other. Not a victim, but perhaps, a Champion."
the comma pushes us down into the story, and the whole stack can be popped by the champion punchline.