Audio problem: When Halloran and Hunt are discussing orders from the commissioner to exhume Jigsaw, it's clear that several of Halloran's lines have been looped in post. His voice is a bit too loud and a bit more forceful than he appears to be speaking, and at least one word doesn't quite line up with his mouth movements. It can be hard to spot the first time, but if you look for it, it's noticeable. (Confirmed in DVD/Blu-Ray commentary - the actor lost his voice and his lines had to be looped).
Audio problem: In the ending scene of the movie when Missy Armitage stabs Chris Washington in the hand with a letter opener, you hear "mmm...yeah" in Chris' voice but his mouth never moves.
Audio problem: When Richard is running around the house trying to find Jen near the end, he is heard ferociously breathing and grunting. The breaths and grunts appear to have been dubbed in as Richard's facial and chest movements remain mostly still, which wouldn't happen if he was breathing and grunting that heavily. (01:41:10)