Real quick I want to say I have little knowledge of the Eco boost and I know they come with their quirks but every time I start my truck I get a slight rattle under the hood (2-3 seconds). Tonight I popped the hood and had my wife step on the gas and you could hear it rattle even more.

also when slowing down (with brake or in coast) once I’m under about 15 mph I get a weird almost grind vibration underneath. Possibly drive train related?

any advice helps. Thank you. (I tried posting a video but had some issues, sorry)

 

Grinding could be the IWE failure that many of the 4x4 folks experience. If not the IWE, 2nd thought is the front differential bearings being faulty.

Take it in for a TSB. If the TSB doesn't correct the grinding then they will do a warranty repair of some IWE related items after a thorough test. They will 'fix' it, but you'll probably not actually be fixed. Next they will rebuild the front differential.

I don't have any input on your rattle question.

 

The rattle is probably the timing chain.