Include

[balloonfoot]

I'm with Cool_Canuck. Here's what Ford has to say:

In some cases, drivers may notice a "cackle" sound while the engine is at idle and normal operating temperature. The cackle sounds like a rod knock coming from the driver-side rear of the engine. Typically, the cackle noise goes away when the driver accelerates off of base idle, and returns again when the vehicle stops or rests at base idle. Cackle often can show up at about 1,200-rpm under a slight load, not just at idle. A true cackle sounds different than familiar "knock" diesel engines make during normal combustion, which is loudest when the engine is cold. Unlike the knock, the cackle will come and go intermittently (at idle, versus while driving) and will increase in intensity as the engine warms up to operating temperature.
A cackle concern can be annoying, but be assured that it does not damage the engine or decrease the engine performance or fuel economy
In mature vehicles, it is likely that the onset of cackle can be traced to a loss of fuel pressure caused by:
• A restricted fuel filter.
• A fuel pump failure.
• Air injected into the system on the suction side of the fuel system

My '02 cackles when it's warmed up and usually at or near idle. No noise when cold or at higher RPM's