GM-GMC: 2003 Gmc Envoy, gmc envoy, exhaust gases

Question
I have a 2003 Gmc Envoy 4.2ltr 6 cyl. 4 wheel drive. It has 74,000 miles. Recently the car has gotten louder and today seems to idle rough when the brake is pressed and it is put into gear. When it drives there is no real hesiatation of roughness but the car seems to get louder. (almost like the exhaust has a hole in it) The check engine light came on and I had it checked out the original diagnosis was a loose gas cap. That does not seem to be the problem though. Any help would be appreciated. Thanks

Answer
It is possible that you have an exhaust leak, typically they will get louder as the engine warms up and things expand.   Use a light and see if you can see any bolts missing or black marks where exhaust gases are coming out where they shouldn't be.
hope this helps