This randomly started on the way out of town for a trip last Monday, about four hours into the trip. I've never heard this sound before or after on this truck. I've had it for 9 years this past August and by the time the noise started, ~231,500 miles of very trouble-free ownership.

After driving with it the first day and into the second, we ended up putting another 2000 miles on the truck, returning back safely last night.

It's a bump / thump that you can hear through the floor board. It almost sounds like it comes from the front of the motor, but my Pops (riding shotgun) said it felt like it was under his seat! Apparently it's loud enough for bystanders off the road to hear as we caught their attention passing through a town. It's almost like it comes from the left side sometimes and the right side others.

It has no effect on engine performance, fuel economy, engine idle characteristics, transmission performance, transfer case performance, steering, suspension, etc. This was a 2300 mile trip and ~400 miles of that was off road with a lot of that in 4WD in the Rockies. Of that 2300 miles, it was everything from crawling speeds to 75-80mph highway speeds. At the low speed driving and crawling speeds, I don't remember hearing the mystery bump. Once we got up to any kind of cruising speed however, it would randomly show up and go away. Very randomly...

There were times where we went more than an hour or two without hearing it, then it would randomly happen repeatedly but with no pattern to its frequency or duration. Speeding up and slowing down, RPM up / down had no effect on the bump frequency either. For example...cruising at 75mph with the random / periodical bump, slowing down as you come into a town, cruising through the town, then returning to highway speed as you leave...and with all the RPM changes associated with it...no effect on the bump. It made its noise when it felt like it. I will say that at the lower speeds (not RPM) you could hear a more pronounced noise that I assume was causing it to sound like a bump at faster speeds, but I still couldn't identify the source.

We listened to it at idle with the hood up, running and holding at various RPM, letting it return to idle, A/C on, A/C off...nothing. Runs like a Swiss clock, no leaks, etc.

At no time, when it "bumped" was there a change in RPM, any kind of surge / stall...NOTHING. That was what seemed strangest...that there was no operational difference, or change, or anything that occurred when the noise happened. We ended up driving over 2000 miles with the bump with no problems. We crawled all under the truck checking everything we could on that second morning, but everything looked about as perfect as it could be. We've both done our share of shade tree work on vehicles over the years, but this one has us scratching our heads. He actually has my old 2014 F-150, which is nearly identical to my 2016 and he's never experienced this with his either.

Now that I'm home though, I need to figure this out because one of the kiddos is about to buy this truck from me!

 

Just thinking of the possibilities here, in the area you describe. Sounds like the output shaft splines for your rear driveshaft might be dry. Maybe a bad U joint, at the differential, or a sloppy pinion. All of which would cuase a clunk in the driveshaft, and make you feel it under the floor.

 

I have one that the torque converter causes the whole truck to shake and rumble. feels like you're driving on the rumble strips only worse.

 

Had the symptom you describe on a van and the problem was a bad U joint, it had no grease in it at all!

 

This sound kept coming from the front of the truck, sometimes more left, sometime more right. Within a couple days of the first noise, the shutter actuator starting tick*tick*ticking. So naturally, I was thinking...great, what else is going to suddenly starting acting up?

When I got back last week, my shop manager (who used to be a mechanic) hooked up his scanner. Actuator codes on the shutters...

Just so I wouldn't have to hear the ticking anymore, and to prevent further damage to it, I unplugged the actuator while we had the hood up. That was a week ago and the mystery noise stopped as soon as I unplugged the actuator.

These gremlins y'all...strange...

 

Hard for me to imagine how the shutters make a thump sound.

 

I agree. It's very strange! There's a definite sound that's not a thump coming from the front but also the muffled thump you hear in the cab. It's a new one for me. The only thing I'm certain of though is that it has not happened again since I unplugged that actuator a week ago.

 

Plug it back in and see if the thump returns.

 

Out of curiosity check the hanger bearing as it may be on the way out