I have a GMC Envoy. It suddenly started running loud. It is like cranking an old diesel truck now instead of my quiet suv. The sound seems to the near the base of the motor where the exhaust system starts. Once i get up to speed, the noise dies away.
Sounds like (see what I did there?) an exhaust leak, get it looked at soon.
Had a friend with the exact same problem, for him it was a bad exhaust manifold.
Right these are notorious for getting cracked exhaust manifolds. Have an Isuzu Ascender which GM made and is the same vehicle and this happened to mine , luckily they stepped up on any 2008-9 models and had an extended warranty on them and they picked up the bill . If you have to pick up the bill you are looking at $800-1000 to replace it .