Help tracking down engine noise

2002 2.7 Auto, 4x4.

It's not a ping or knock or tap sound, to me it sound like a whirling or growling sound. Consistent with engine RPMs. No check engine light, no noticeable change in performance. Started about two weeks ago and in recent days has gotten louder (or I'm paying more attention it, not sure). I don't drive it very much though. It is not the power steering or AC compressor, but it is hard to localize where the sound is coming from. I hate to direct you away from suggesting other things by asking, but I know there is a spring loaded gear that drives the exhaust cam, and this sound reminds me of more of a gear sound more than anything. I am not sure if I am correct to think that spring in the gear is to keep tension between the gears and I wonder if that spring were to fail could it cause this sound. Can you think of anything else I could check? Any trouble with balance shafts in these engines? Another area I don't have much experience in is Automatic transmission trouble. All the Auto cars I've owned never had any transmission problems for me to diagnose. That said, could a torque converter make this noise? Remember, it follows engine RPMs not speed of the truck. Let me know what you think.

 

um are the front wheels locked? Change diff fluid, grease ujoints, check wxhaust manifold if its leaking.

 

Double check all your pulleys up front......
especially the biggest/lowest one.......the one mounted in rubber......
harmonic balancer.....

 

I mentioned it is not speed dependant, it's engine RPM dependant, so not a drivetrain issue. Thanks.

The harmonic balancer has no moving parts, so itself can not make any noise other than rattling if it is falling apart. That leaves AC, Alt, tensioner pulley, fan and PS. I will try removing the belts this weekend and see if the noise goes away. Thanks.

 

Video of noise.
https://www.youtube.com/watch?v=O9ylIb4DfyE