Fat Daddy said:
I thought of that, but fire damage from a flaming sword can't be cancelled by a Silence spell either, sonic damage from a screaming weapon can be.
Arguably, a Flaming Sword cannot be used underwater whereas a Screaming Sword can.
But, the balance point here is that of facing opponents with certain abilities.
Sure, you could face an NPC Bard or Cleric who has a Silence spell. But, would they waste that on a PC with a Screaming Sword, or would they use it on a PC spell caster? Who is more of a threat?
Ditto for Protection From Energy Sonic. If an NPC spell caster has a chance to cast Protection From Energy, how often is it real useful to protect versus Sonic due to one PC with a Screaming Sword compared to the PC spell casters who most likely will not use Sonic damage, but rather Fire or some other form of damage?
Ditto for Monsters. The Screaming Sword always damages the vast majority of Energy Resistent monsters. The Flaming Sword may or may not.
I understand that Silence was added as a defense against the weapon, but this hardly changes the game at all. The vast majority (95%+) set of encounters (in most campaigns unless you are always fighting temple minions), NPCs will either not have (the highest percentage) or bother with a Silence spell for this circumstance. Even if an NPC has the Silence spell, the Screaming Sword should be the least of his worries.
And if a spell caster silences an opponent with a Screaming Sword, the opponent can move up to the spell caster and attack in a Silence field (hence, preventing most of the spell caster's spells). This could easily be more of a hindrance than a help.
The game rules should be consistent. Sonic attacks (almost always) do less damage than Flaming attacks precisely because there are so few defenses against them (btw, Silence protects against all other sonic attacks as well).
Balance-wise and consistency-wise, a Screaming weapon should be +1D4 (just like other Sonic attacks) and it should still be stopped by a Silence spell (just like other Sonic attacks) for +1.