rattle rattle thunder clatter boom boom boom...

[05crewcab]

Strange thing started happening this week...

When my truck is moving and under load, (accelerating, driving up a hill, etc.) I have this rather loud clattering noise coming from someplace in or near the engine bay. It doesn't happen if I don't have my foot in it, and won't make the noise in Park.

I crawled under the truck tonight and checked everywhere for things touching the drivetrain...exhaust hangers, trans cooler lines, kickdown cable, speedo cable, PS lines, loose brackets, starter, etc. I also checked and greased my u-joints and the carrier bearing is in good shape.

Anyone have any ideas on what to check next? The motor sounds fine when revving in Park, and doesn't make this noise at idle or over 3000 RPM... I'm stumped.