https://drive.google.com/file/d/1d26...EEXDBsjj5/view

click above link for a video clip to hear noise.
this noise is not constant, it only happens maybe 1 out of every 3 drives when empty, but more common when hauling heavy load. ONLY happens when accelerating in 3rd gear, or when going uphill or when loaded. stops when i let off gas. occurs around 1800-2100 rpm when empty. sometimes when i hear the noise it seems im not accelerating quite as well as i should be. stops as soon as i shift into 4th. definitely coming from the front of my truck. 2000 v10 f350 automatic with 90k miles.

ive heard 2 theories; vacuum leak or failing u joint.

 

 

I couldn't get the link to work either.

Somewhere in the back of my memory I recall an instance where the alternator vibrated and produced a mysterious noise. There was an addl piece added to the mounting to correct that problem. It may or may not apply here, but I thought I would mention it . If, the vibration is producing a noise that the knock sensor(s) are picking up and the PCM is retarding timing, it could explain the sudden power loss, I don't know.
This does go back a bit and I don't remember if they just unplugged the alt or used a different belt by passing the alt altogether to take it out of the picture. If no other cause is found , it might pay to consider the info.