When i accelerate my 2017 Ford F150 3.5 4WD, at speeds over around 50, i often hear a very fast rattle. What i’ve noticed is it will go away after putting it into 4WD. Just wondering if anyone knows what it is.

 

Welcome to the forum. Lets see the truck.

 

My guess, it is iwe related. Common issue. Do you have 4A (Lariat and above)? Many times it is a simple iwe check valve, pn yg-360 on amazon, I've replaced mine 2x.

 

Yep its has 4A, How easy is the fix?

 

Well, hopefully easy... Starters, drive around a couple days in 4A. Does the sound go away? If yes, start with the basic check valve right by the brake booster. Buy p/n I suggested, or go to autostore, or the real Ford Version

Amazon
Typical location pic below. There certainly are many tests, but if your sound stops in 4A, often it is this

 

Changed it last night, drove today with no rattle! First time in months. Your the man, Thanks for the help

 

One mans rattle, is another guys squeak, and another guys roar, and another guys,,,,,,,,,,,,
Obviously it sounded like this?