2004 Ford Ranger Exhaust Rattle

When my truck is not running you can get underneath and hit the exhaust pipe with your hand and you will hear a rattling noise no loose sheilds or anything like that but sounds like it's coming from inside the exhaust. When started and idling it is a constant metal sounding rattle at speed on the highway with the windows up and radio off you can hear the rattle also seems to coming from the front part of the exhaust around the convertors.

Thank you for any help you may have for a fix on the "rattle"

Keith Banister