So my 2018 has developed a strange "thunking" sound when the truck shifts directions horizontally. Basically, I can push on the the rear passenger tire from one side causing the truck to rock back and forth and a weird metal panel "thunking" noise can be heard. It's not coming from the gas tank or the spare tire, it is definitely coming from the bed but I can't seem to narrow down an exact spot. It's the kind of sound a piece of sheet metal makes when it is floppy. Might be a loose panel or something but everything seems to be tight. Wanted to see if anyone can replacate this sound on their 2018... Its going to the dealer Friday to be looked at because it's annoying as hell. sound clip on post 4

UPDATE: See post 18. Problem solved.

 

There is a known noise that comes from the rear leaf springs when driving over uneven surfaces. Basically the Leaf Spring bushing is binding up and letting go, causing the noise. If this is not your issue and it sounds like it is not, from what your describing it almost sounds like the body panels are flexing.

 

You are probably hearing the end play in the axle shafts. This is a normal sound of the floating axles moving in all differentials that secure the shaft at the inboard end with a "C" clip. Some seem to have more end play than others but it is not an issue.

 

here is the noise: I'm pushing on the rear tire and causing the truck to rock back and forth. the noise cannot be heard when pushing down on the rear bumper and working the suspension up and down.

 

I have a 2018 f150 4x4 lariat and I'm hearing the same noise, any luck figuring out what it is?

 

 

Likely this. I have it and it seems somewhat common.

https://www.f150forum.com/f118/clunk-rear-truck-306127/

 

It's the leaf springs. I had 1 leaf pack replaced under warranty. With help from members on this forum I narrowed it down to the leaf spring isolators. Easiest thing to do is get a flat head screw driver and pry the leaf back just enough so you can spray some grease or Fluid Film in between. This basically silences them for a while.

 

Have you checked that your spare tire is cinched up tight in the well? If it's dangling from the chain at all, it'll bump back and forth and make a sound. Might as well check the air pressure while you're under there.

 

Oh yeah. It's the leafs because when I sprayed some Fluid Film in there the clunking stopped and has remained quiet for the last 2-3k miles. I figure I'll get under there every oil change and spray the isolators.