Two problems related to manifold/header/muffler/tail pipe have been reported for the 2004 GMC Envoy. The most recently reported issues are listed below.
The contact owns a 2004 GMC Envoy. While the vehicle was stationary, the exhaust manifold fractured and the heat from the exhaust manifold damaged the frame of the vehicle. The contact stated that the failure caused severe rust and corrosion. In addition, the contact stated that there were holes in the frame. A dealer was not made aware of the failure. The manufacturer stated that the failure was not safety related and there were no recalls on the vehicle. The failure mileage was 136,000.
Exhaust manifold cracked. Gm has a special extended warrenty on model years 2008-2009 only. Yet they are the same manifold and same engine on all model years. There are 100's of reports of cracked manifolds online, with all model years.