I noticed Whispered Truth when looking through the Req list and I believe it is Buck's ODST pistol. The reason I am not saying it is the Halo: CE pistol is because 343i said they didn't add it in yet. Also, Whispered Truth sounds like a Silenced OP weapon.
I just got the certification for it tonight. I haven't got a chance to use it though. It is an Ultra Rare Mythic Req. It is silenced/suppressed and increases movement speed and is also a three round burst.