When it comes to undesired noises, silencing guns is the same thing as silencing incessant yammerers. It all comes down to dealing with hot gas.tl;dr version: Silencers don’t “silence”. They muffle one cause behind the noise of a gunshot, but they can’t do anything against the rest of the noise. If you want real stealth, call Hawkeye and use his crossbow.
Extra credit: There’s a fantastic, absurdly detailed chapter — seriously, it went on for pages — in Tom Clancy’s Without Remorse in which John Clark manufactures a suppressor in his machine shop. (Plus the book is riveting.)