that is the phasers. two seconds of marbles on a cold start, quiet once oil pressure is up, no light. it is the locking pin in the variable cam timing phaser not holding while the engine builds pressure. 2017 to 2020 3.5 EcoBoost is the range, and yes there is a TSB, 21-2315, which replaces both phasers and the VCT solenoids and does a PCM update. a lot of trucks got it under the 5 year 60,000 powertrain. at 71k you are past that unless you bought an ESP plan with the truck in 2023, so dig out that paperwork.
cost out of pocket: at our store it is about 2,400 with the updated phasers, solenoids and a look at the timing set. a good independent that has done a few of them will be 1,600 to 1,800. do not let anybody sell you a chain and guides on top unless they show you a stretched chain, most of these at 71k are fine.
can you tow on it: yes, for now. the rattle is not eating anything today, it is telling you the pin is worn. what you do not want is another year of cold starts, because then the phaser starts working on the sprocket and the job grows. get it done before it is 20 degrees in the barn lot every morning.
put your VIN into the owner side of ford.com first. it shows open recalls and any customer satisfaction program on your truck and it costs you nothing.
