I have a weird intermittent noise that I recently noticed on my new 2018 XLT, 3.5L EB, only 1550 miles on it. A couple of times now when I turn the key and start it there is a noticeable "thunk" up front. It really isn't regular.....yet! and funny it has never done it during the auto stop restart, only when turning the key.
Any ideas? If it continues I will bring it to the dealer but thought I'd throw the question out here. Thanks

 

I have the same thing, it seems to happen once the truck is at operating temperature only with the key or remote start, never on a cold start and not when the auto stop start is working either. I though it might have been the drive shaft turning during start (there is a long thread on that) but when I finally got under my truck, the drive shafts do not move when the "thunk" happens. it seems to be coming from the transfer case but not really sure and mine is a 2018, 5.0 4x4. Interestingly my son's truck, which is a 2wd 2018, 5.0, has not done this. I am having mine worked on this Friday (software updates for transmission, and engine rattle) and will have my son look into the noise. He is a Ford Tech in training (has one more semester to go) so maybe he and his mentor can come up with a reason.
It has done it pretty much from day one and after 20k miles there does not seem to be any affect from the noise so far. I was hoping what ever is making the "thunk" would just go ahead a break but not yet.

 

Interesting,... mine is an FX4 so sounds like it may be something with the 4 wheel drive. It is coming from somewhere under my feet. Please keep me updated if your son finds anything. Thx

 

https://www.f150forum.com/f118/singl...engine-383628/

 

thanks for that. Didn't think to search, who would have guessed it was a common issue