I searched the forums, but did not find anything exactly like my problem.
I have a 2006 HHR, 2.4L, Auto. When you accelerate, you can hear a hissing sound. I cannot tell if it is from the exhaust or an intake leak. I checked the exhaust and did not see any leaks. As soon as you let off the gas, the noise goes away.
The car also surges when driving. You can watch the tach bounce as you slowly accelerete. If you step on it, it does not seem to surge. Not sure if this would have something to do with people talking about reprogramming the TCM or not. Spark plugs have been replaced.
No check engine lights. Fuel mileage has also seemed to drop with these issues. I did ask my local dealer if they have heard of this, and they have not. Any help would be appreciated.

 

vacuum leak or cracked exhaust manifold could be the culprit... you need to get it in so a dealer/service place can see and hear the problem for themselves.

 

I am experiencing the same problem. Took it to Goodyear and they could not hear it. I get the sound at startup in the morning and during acceleration. Mine is a 2007 with 93,000. Gonna take it to the dealership soon. I will let u know what they tell me.