This groaning sound can also be reproduced when in 3 rd gear. When I slow down there is no groaning sound. 'm concerned that this might be a beginning of a major problem. Is this engine related, or is it caused by the exhaust, transmission. I had a similar situation on a truck and the dealer installed weights on the exhaust to eliminate that noise.
When accelerating there is a groaning sound at 3200 rpm on 2008 Pontiac G6
If your noise is only limited to specific engine load conditions then it could very well be related to the exhaust system. It may be a good idea the road test your G6 with a technician from your local dealer to try and determine to cause of the noise. I don't fine any service bulletins for exhaust or engine noise on your G6 at this time.