ndavidsusan

Have 2001 4door sedan. When first starting in morning and putting veh in reverse to back out of driveway onto street, there is loud rattle, clattering noise coming from somewhere under the engine. Have had son push and pull on exhaust items (pipe, cat. converter and muffler) and they seem to be secured properly. When put into Drive, the noise goes away. After driving a while, when having to back up, the noise is almost completely gone. Any ideas?