Read some threads, didn’t quite find this predominantly. 2018 5.0 XLT, 160k. Rebuilt 10R80, that runs fine. No start up rattle, some idle noise, don’t know how much to expect, no decel rattle, none ever noted on grades or acceleration. Setting up weight distribution on 3500 lb travel trailer, drove a 10% grade at low speed. Accelerating in tow haul, distinctive engine rattle at light acceleration possibly 1500-2k RPM, immediately goes away with more power applied. Since used with limited service records other than dealer oil changes about every 5k, my history and knowledge of this is very limited. Intake runners fluttering?

 

my guess would be wastegate rattle i have a noise that sounds very much like valvetrain noise diagnosed as wastegate by ford service dept

 

more checking to do. No CEL, have to look for other codes, but recent forscan operating check didn’t reveal anything. I understand the possibility of defective or broken intake runner may not code.