Villain has been raising my c-bets with air, and I think he could be raising for a free card here. Do I lead the turn, or check-call down?

Party Poker No-Limit Hold'em, $ BB (4 handed) Hand History Converter Tool from FlopTurnRiver.com (Format: FlopTurnRiver)

Hero ($92.43)
Button (villain)/ ($89.30)
SB ($300.38)
BB ($96.40)

Preflop: Hero is UTG with A, J. SB posts a blind of $0.50.
Hero raises to $4, Button (villain)/ calls $4, 2 folds.

Flop: ($9.50) 4, 6, A (2 players)
Hero bets $6, villain raises to $12, Hero calls $6.

Turn: ($33.50) 3 (2 players)
Hero??