No you can't stifle it. Here's the Crystal Keep Ruling:
406 - Mana Abilities
* 406.1 - A mana ability is either (a) an activated ability that could put mana into a player's mana pool when it resolves or (b) a triggered ability that triggers from a mana ability and could produce additional mana. A mana ability can generate other effects at the same time it produces mana. [CompRules 2003/07/01]
Metalworker
Color= Artifact Type= Artifact Creature Cost= 3 UD(R)
Text (UD+errata): 1/2. ;

: Reveal any number of artifact cards in your hand. Add

to your mana pool for each card revealed this way. [Oracle 2003/07/01]
* You can reveal zero cards to gain zero mana. [DeLaney 1999/06/08]
* This is a mana ability. It does not go on the stack and cannot be responded to. [DeLaney 1999/06/08]
That should clear it up. I'll add mana abilities to my rules FAQ above.