Good morning,
If that is coming from the converter, the insides of the converter are melted and loose and they are moving around internally. The converter will have to be replaced.
https://www.2carpros.com/articles/catalytic-converter-replacement
There was a TSB for knocking which I posted below as well.
Roy
TSB 04-20-6
10/18/04
TICKING OR KNOCKING NOISE COMING FROM THE
CATALYTIC CONVERTERS
FORD:
1997-1998 F-250 LD
1997-2003 F-150
ISSUE
Some 1997-2003 F-150 vehicles equipped with any engine, and 1997-1998 F-250 LD vehicles equipped with the 5.4L engine, may exhibit a ticking or knocking noise coming from the catalytic converters. The noise may be described as sounding like a diesel engine. The condition will be present when the vehicle is in gear at idle only, and is more pronounced when the vehicle is stationary, such as sitting in a drive-through line. The noise is normal, and is created by engine pulses being amplified through the light-off converters.
ACTION
DO NOT replace converters unless loose internal components are found. To reduce the noise, install a wrap kit on each of the light-off converters. Refer to the instruction sheet included in the kit.
WARRANTY STATUS: Eligible Under Provisions Of New Vehicle Limited Warranty Coverage And Emissions Warranty Coverage
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Parts Block
OPERATION DESCRIPTION TIME 042006A Install Wrap Kit On Both 0.7 Hr. Light-Off Converters (Includes Time To Perform Road Test)
DEALER CODING
CONDITION BASIC PART NO. CODE 5E212 42
Monday, March 8th, 2021 AT 2:46 AM