Rattle in resonator at 1000 RPM

[31RamIt]

For awhile now I get a rattling sound from the right side exhaust around 1000 rpm. If I could start the truck and let it warm up until the idle drops, I hear it at that engine speed. Then in parking lots if I’m just barely on the throttle, I hear it. This morning I got underneath while it was idling and as it dropped, I could hear it coming from the area of the right resonator. Can’t tell where though.
Anyone have similar problems?