Does Stony Silence stop Salvage Titan's activated ability from the graveyard?
No, Stony Silence does not affect that ability on Salvage Titan.
Rule 109.2 says

If a spell or ability uses a description of an object that includes a card type or subtype, but doesn’t include the word “card,” “spell,” “source,” or “scheme,” it means a permanent of that card type or subtype on the battlefield.

Stony Silence refers to &quot;artifacts&quot;, so it is talking about artifact permanents on the battlefield. So, while Salvage Titan is in the graveyard, Stony Silence's effect does not apply to it.