1998 V6 engine whistle louder than ever

[Teedeejr]

Good Morning,

I thought I'd take the time to film some video and upload for some assistance, since this engine whistle is now driving me insane. It's been on and off (mostly on) since I purchased the truck almost a year ago. I've thought it was belt driven or pulley driven, but I've since changed the belts and it is still here. I (unfortunately) did not have the mechanic see if it stopped with the belts off. Either way, I'm pretty sure it is coming from the back of the engine near the firewall (as evidenced by the videos).

https://youtu.be/eFuJS1BQOt0


The whistle starts at :15 when I pull the accelerator cable. I can make it change while driving by lightly pressing the pedal and it seems to change in frequency.

https://youtu.be/K96cAmHiprM


The whistle is constant in this video, however, it stopped by itself a second after I stopped filming.

A few details - the truck is a 1998 SR5 V6 2WD with 49 state emissions.
I've had a P0171 code since purchased that I haven't been able to remedy. I've tried a few things but my Ave. MPG over the last year is 18.9 and I my last few tanks have been 19.5, 19.6 & 19.9 so I'm not complaining.

Any thoughts? Ideas? Etc.?

Thanks for any input.

 

[jgue467]

Damn that's loud! Haven't heard on here about anyone else having that but who knows, hopefully someone will chime in.

Doesn't sound like belts. At first I though maybe vacuum leak but that would be a huge vacuum, not sure engine would run so well with that, so probably not. Doesn't sound like anything rubbing either. Hmmmm.

 

[Donny Voodoo]

Could be a leaking exhaust manifold.

 

[Teedeejr]

I paid closer attention while driving at lunch and the whistle stops during acceleration, even in a parking lot or if I press the pedal lightly while coasting.

It also comes and goes on its own, and at lunch, upon startup, it did not immediately begin. Only after a minute or so, did it start back up.

Any hunches, hints, clues or actions I can take to try and diagnose this?