One problem related to engine knocking noise has been reported for the 2012 Chevrolet Impala.
Engine makes a knocking noise while accelerating. I drove another one and the noise was even worse, that one had 15000 miles on it. This seems to be a common problem with them all. I am very unhappy with this car. I don't enjoy hearing all this noise from a new car. (now has 6000 miles on it) if I can't resolve this problem it will be the last gm car I ever buy. The dealer had me drive another new 2012 Impala when I mentioned the noise, it also sounded the same. Gm definitely didn't address this problem before production.