According to Classical Indian School of Logic, the argument 'Sound is eternal because it is produced' is fallacious because:

The reason 'because it is produced' actually establishes non-eternality, the opposite of the intended thesis of eternity.

Whatever is produced is regularly seen to be non-eternal, like a pot.

So the middle term proves the very contradictory of what is to be shown.

A middle term that yields the opposite of the sadhya is a contradictory middle.

That is why the classical school judges this inference fallacious as viruddha.