Same problem as the gentleman in NY is complaining about. There is a "muffled" sound, like a mis-fire internally in the intake manifold... Can be at highway speeds, also, engine temp doesn't matter, seems to do it mostly in second gear. When you let off the throttle for a moment and then get back in the gas is when it makes a huge hesitation and then makes the sound... It can even do the noise two quick times in a row.

There has been a clunking noise in the front end of the 2012 Impala LT. The dealer identified the noise as back lash in the engine and transmission when making slight gas pedal adjustments, like in city driving. The car is at the dealers a second time for the problem. The dealer hasn't found a fix for it yet and says that the backlash in the engine and transmission is within specs. I don't know what that means, but the dealer has provided a loaner as they look into it further.