rattling noise! please help

[RedDye01]

Alright i need your guys help. I have an 01 psd and when i start it cold i can hear a light rattle behind the dash. It sounds like a folgers can wrapped in duct tape with a ping pong ball inside being shaken. You cant hear it when accelerating but when your doing 40 or so and take your foot off the gas you can faintly hear it. You hear it most when you shut the motor off. After the motor shuts off you hear it for about half a second and its gone. What could it be? I stayed toward the front of the hood by the motor and a friend turned the truck on and off and i couldnt hear anything from the engine bay. any ideas?

[RedDye01]

bumpppppppp

[smitty16s]

does the wts light flicker when you hear this rattle?

[RedDye01]

what is the wts light?

[smitty16s]

the wait to start light

[RedDye01]

no not that i've noticed but im gona go try now...... no no flickering light. If i were to guess where it was coming from id say it sounds like it comes right where the bottom left corner of the windshield meets the dash. Rattly ping pong ball.

[smitty16s]

is the windshield coming apart from the seal?

[RedDye01]

na its on there good. it sounds like its coming from under the dash but i dont know what could be under there that would rattle. i cant see anything when it take off the fuse panel cover

[smitty16s]

pull the dash around the radio and gauge cluster, its really easy just a snap on/off see if you can see anything back there.