Ok, but if it does it again - before you start the truck try opening and closing all 4 doors.
I would also add open the hood, but you have already done that.
Due to the location of the sound from the video's - If this is not a Tracking Device then the only logical thing that makes sense is the - Alarm Horn
The Alarm Horn is sounded, when you use the FOB and press the lock button (2x)
The Horn will give you a quick (honk) and the exterior lights flash.
The Alarm Horn will also sound (If the truck is locked) and any door or hood is opened.
If you have the Perimeter PLUS system (Dealer Install-Aftermarket Up-Sale) then this adds a vibration (shock) sensor to the system - It is intended to pick up the breaking of glass
The Door Inputs for the Alarm come from the Door Ajar Switches, if any of those switches are faulty or dirty - it may be generating a false partial power to the circuit, hence not full power to actually trigger the full alarm tone.
The Hood Ajar Switch does the same, but since it has been opened for the video's, I think we can eliminate it.
Now I know that most likely that the truck is now unlocked, and the alarm should be disarmed.
during your investigation for the noise.
But a What IF? scenario comes into play, and that is a sticking Alarm Relay.
So, just curious if opening the doors one at a time, would get the noise to stop.
also
Try - Pressing the FOB - Lock Button (2x) to force power on the Alarm Relay
Starting the truck makes it stop, but just trying to help pinpoint exactly where it is coming from without pulling panels / covers from the front end.
Is is your normal (Procedure) to lock the truck from the FOB until you get the Feedback Horn?
If so, This MAY be a clue - as the very last thing you have done was activate the Alarm Relay.
FYI - It does not have to be (2x) locked to get the alarm to arm, this is only for owner convince as it provides feedback (Yes-Locked & Armed)
So, thinking outside the box, if the Alarm Relay was sticking there is constant power to it, and it shares the same wiring circuit as the TCU, if the TCU were to power up then the Alarm Relay is stuck would see residual power and the beeping you hear could possibly be the TCU doing a Check Up communication to the truck and you are actually hearing the power being applied.
Note: The TCU = Telecommunications Unit, this is the module that links the Ford Pass to the truck and also Links the Sync Update via OTA Updates.
This is also the module that provides the informational messages to Ford Pass, Deep Sleep, Modules Turned Off to save battery power etc.
So, to sum it up, the TCU will periodically power up on its own with the truck off.
I would be curious if you were to check the Ford Pass App, and note if the last update time on the App matches the time interval of the beep,
You may also try - Pulling Fuse #8 (Cabin Fuse Box) by your left knee - 10 Amp - Anti-Theft Alarm Horn and see if the beep stops.
Did yesterday, I lock my doors with the finger on the door handle, I usually don’t lock with fob. Truck locked came back to the truck and heard it again. Usually 30-33 second intervals
