Randezvous exhaust noise

Just bought a 2003 Rondezvous (3.4 V6 CXL AWD 100,000 mi) runs well except for a very loud muffler-type noise when you reach 22-2300 RPM, and only at that time. Before and after these RMPs are fine. Only makes noise in drive, not in park or neutral. It is not general road noise as far as I can tell.