If silence had a scent, it would smell like a puzzle. The old musty smell when remaking a favorite or the smell of a freshly open bag of pieces, pieces that still have shavings of paper because they weren't cut perfectly during manufacturing.

Or silence could be the smell of freshly mowed grass. When the mower is grinding away at overgrown grass all of my thoughts are drowned out and I find that my mind grows silent when my nose is full of the scent of grass that is defending itself against a monster attacker.