Is this knock something that happens when you're in park and reving? Or is it only when you are driving? Does the knock stop at idle when your moving, as in coasting down the road in neutral at a decent speed?
When you rev, the motor will torque to once side, something might be touching, possibly a broken motor mount? Bumps could be making something that is loose tap against something.
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'04 3500 Laramie SB QC 4x4 305/555 CTD, 48RE, AFE Stage 2 CAI, 4" Aero 4040 Turbine, Banks Six-Gun w/PowerPDA, Tone Ring Mod, 35/12.50/17 MT Baja Claw Radials, 2" Leveling Kit