Rattling Noise?

I have a 2005 2500hd extended cab with the 6.0 and auto trans, 70,000 miles. At idle in gear I notice an annoying rattling sound coming from underneath. I assumed it was a heat shield until I ran it up on ramps and got underneath with the engine running and in gear. It sounds as if it's coming from the torque converter. I am the original owner, have no transmission problems (yet) and the truck has never been abused. Has anyone else encountered this? Is it normal?

Could your flexplate be loose or cracked? Can you remove the cover and take a look/feel maybe? Just thinking...

Good thought, I'll have to check that. Thanks.

Is it a rattle or does it sound more like a bolt being thrown around in the bell housing? If it's the latter, check the starter gear.