We have a 2006 and 2010 LTs, 2.4 engines. The 2006 has 58K miles, the 2010 has 27K miles. My wife's 2006 engine makes a noticeable "whirring" sound, especially when accelerating that is absent on my 2010. Both get about 27 MPG, but I always notice this when I drive my wife's HHR. Anyone else experience this?

 

Wear on axles and tranny possibly?

 

Small crack in the flex pipe?

 

does it when the air conditioning is on/off?

 

Similar to what a Japanese bike makes?

 

Some interesting inputs -- thanks. It does make a sound similar to a Japanese bike. The 2006 seems to run fine, just very noisy compared to the 2010. I need to confirm but think the sound is there with AC on or off. Seems to shift without issues.