My 240 (running GREAT since I changed the AMM) has a few manifold/exhaust/heat shield rattles/harmonics or whatever you want to call them. Been tracing them down and curing them one at a time. Took off the heat-riser and shield but it was still there. By manual probing I sound that the EGR pipe, where it attaches to the manifold was loose even after torquing the compression nut that holds it.
I loosened the nut and removed the adaptor from the manifold. A beautiful piece of stainless steel hardware- nice touch! I cleaned it up ad replaced it but still the pipe was loose in the fitting, so...
I took a piece of +/- 10 or 12 ga. copper, solid-conductor wire, removed the insulation. I measured the diameter of the EGR pipe and found the next size smaller drill bit. Put the bit in a vise and wrapped the wore around it two or three times, making a sort of copper spring. After tightening the coils I cut along the top, across the coils, making a set of round, copper washer/spacers.
I took one of them, opened it, put it around the pipe, and tightened it with locking pliers until the compression nut would slide over it. This gave the compression nut the ability to hold the EGR tube tightly in the fitting and that noise disappeared.
Wire ends up back inside here V ________ Copper wire |________| V ________
--------------------------| |--||-------| |