Hello Markdrivesford,
I'm not sure if this will help, but my '08 6.4L makes a strange noise from time to time as well. Sounds almost like a slight grating or grinding noise. Also, when I turn off the engine, it will make a huffing sound like air rushing through a hollow tube. This only happens when the truck is attempting to go into regeneration mode, but my constant acceleration and braking prevent it from fully clearing out the diesel particulate filter. Try driving the truck for a short distance to warm it up, and then just park it in the driveway. Leave the engine running and wait for it to go into regeneration mode. You'll know when this happens, because your RPM's will go from like 700 to about 1100. When the truck finally returns to its normal idle speed, the DPF will be fully cleaned. Then try driving it around again to see if the noise is gone. Hope this helps.