Sudden onset hissing noise, RPM dependent

Hi all,

Hoping someone may have some input on a weird noise that arose today on my truck, tried to lay it all out as simply as possible below:

Truck:
- 2016 TRD Sport 6-Speed XtraCab (V6)
- Single owner (bought it new)
- No Mods
- All maintenance has been done meticulously, all fluids, greasing, oil & filter every 5k, etc. (though serp belt is original)
- 168k on the dash
- Never been tached out once, never really been wheeled or abused at all, >80% highway miles, never missed a shift (I know that sounds like BS)
- Truck has always lived in Northern New England (harsh winters, salt, potholes etc.), but only on bumpy dirt roads for the last year
- I do drive fast on the highway (cruising @ 85mph for hours) but never abuse the truck, the only thing I go through on vehicles is Tires usually (get 20-30k vs some people's 40-60k) due to spirited driving in the corners

Issue:
- Sudden onset of a loud hissing/leakage noise any time over 2,500rpm
- Noise occurs both stationary and moving
- With hood popped and a wiper wedged on the gas, I sat it at 3,000rpm and listened around the engine bay
- At first I thought maybe a pulley or the alternator was going bad but the noise seems to be coming from the rear of the engine bay, and more on the passenger side
- No noticeable power loss though MPG has been 1-2 down on average over the last 3 months
- In one day the truck went from fine to sounding like shit when I touch the gas, now I can hear it whenever the windows are down and I'm not on the highway

Circumstance:
- Live in a rural area with bumpy dirt roads for the last year. Drove 100 miles of interstate to "the city" today and as soon as I was driving through town I could hear the noise echoing off the buildings, overpasses, etc.
- Checked all fluid levels and all are fine, changed oil and filter a week ago. Levels are good.
- Repeatedly stopped, popped the hood, propped the gas and listened and the hissing noise was replicable every time as long as it was over 2,500 rpm.
- No obvious noise under ~2,500rpm
- Noise occurs the same whether moving or stationary, only depends on rpm and gets worse as revs increase (I won't rev it over 5k so that was as loud as it got)
- No CEL or other obvious issue
- Checked underneath, no one stole my cat, exhaust run looks fine under the truck, no fluid leaks, etc.
- Lastly, I stopped at a big box store for a propane tank (unrelated) and the tech working the tire shop is a big toyota guy and came out and listened. He said he was 100% sure it was a leak at the header/exhaust manifold on the passenger side, but I have never seen or heard of a single person have that issue in a gen 3 that was stock. Also it was weird how it came on so suddenly, truck was completely fine yesterday.

I will try to figure out how to post a video of the sound moving around the engine bay, but in the meantime I appreciate any and all feedback, possibilities and suggestions on how I can diag this issue especially if it is an exhaust/manifold leak. I can't figure out why the hell I would get a sudden change like this but here I am.

Financially it couldn't have come at a worse time so I'm trying everything I can to keep from turning a shop loose on it.

TIA for any ideas or info

 

My initial thought is a vacuum hose leak. I read your whole thread but didn’t see anything about checking hoses (sorry if I missed it). Ya might try that as well, hard to say without sound/video.

 

check the air intake hoses. make sure they are clamped down properly. it does sound like some sort of vacuum/air leak. if it's not on the intake side it could be the exhaust manifold like the tech said.

 

It definitely sounds like a noise on the intake side of things, if it were exhaust related, i would think the noise would be different, though i could be wrong.

 

Thank you all for the replies so far.

Update:
- Checked the intake side from the air filter (clean and clear) all the way to the intake manifold. All hoses are tight and seated on that end.
- When I changed the oil last week I did notice a tiny (altogether barely equivalent to a grain of rice) of tiny metal in the filter can. I doubt this has anything to do with the issue given the mileage and most people I doubt would have even noticed it if they were looking, just wanted to give full info.
- The noise is not subtle at all. At 1,400rpm, the truck sounds like it did new. At 2,600 RPM, it sounds like it wants to explode with the amount of noise coming from this hissing sound. Driving under an overpass or revving it at all is now embarrassing. When I rev it, it overpowers most of the other engine noises even with the hood open, with a dramatic tone shift when I hit that 2,500 mark.
- I had no choice but to drive the 100 miles back home after I found the issue, when I got home it seemed like the noise was 10-15% louder/worse than when I first noticed it but that may be my perception. Hoping no further damage was caused by that.
- I will check for vacuum leaks in the morning but honestly I'm not great at diag'ing those.
- Again, nothing really changed which is why this is so weird. Other than the oil change last weekend I haven't touched or disturbed anything in the engine bay and haven't hit or run over anything either. My best guess as of now is that the bumpy roads I've been driving on along with corrosion have led to a failure in the exhaust somewhere very close to the motor (this is not a downstream noise).

I will post video and audio tomorrow of it at idle and at 3k rpm for comparison and really appreciate the tips. Any more are also appreciated.