What is this oscillating grunting during warm-up?

Seems to be coming from the right side of the engine bay. It is really loud and aggressive on a cold start up, correlating with revvs up and down and sounds horrible when it peaks out, like the car is shaking trim off or something. Quiets most of the way down after the car has been running for a while. It's relatively mild in the video as it has been running for a couple minutes. I have tried ruling out loose parts/trim as much as possible in the bay. Seems related to exhaust to me, as it is a hollow, metallic, high frequency, low pitch buzzing with felt vibrations in the cabin. 215k miles. I have dealt with startup shake due to misfires etc. and this feels different.

Could it possibly be the issue in this video?

 

Sorry I don't understand your first sentiment... And you have a gen 2 also making this sound? Or a different gen.

 

Yes pressing on everything I can in the bay is what I have tried so far. I will go try some stuff again based on your suspicions. In person, the sound seems as if it's emanating from the right of the air box, under the coolant tank somewhere... but impossible to say for sure as it reverberates through the whole bay and buzzes everything. Thanks for the reply.

 

Opposite side that the noise seems to be originating from -- slightly towards the drivers side of the bay. Sorry if "right side" was confusing.

I will reupload the now expired video soon.

 

I did some more listening and now I feel that the sound is actually coming from the engine or something attached to it, near cylinder 4. It is extremely hard to pinpoint because it only happens during higher revs; in maintenance mode the revs are too low on the warmed up engine to produce the sound. I will feel up the valve cover near #4 next cold start.

here is the video that's now a dead link in the OP, until a mod edits it back into the OP:

 

new video, hopefully the sound is more clear as it really flares up towards the end when the engine is getting ready to shut off.

Pressed all around everything, cannot affect the sound at all, valve cover feels normal etc.

 

I can only assure you that video was taken after pressing on all the parts again including putting serious weight on the airbox, and wasn't intended to show me testing parts. Was just fingering around still while mostly trying to catch the sound with the microphone. It's 100% not the air box or anything else visible from the top of the bay, at least not in a way that stops with pressure.

 

Actually already had that on the docket since this is a new-to-me, so did both as well as ran a BG hybrid repair kit. No change in the buzzing aside from a slight volume decrease corresponding with a slightly smoother engine in general after the cleanings and treatments.

I might still have to try this next time I can get a wheel off, as my approximation of the source keeps moving around on me on different days, listening from different angles... as evidenced by my indecisiveness in this thread. I have leaned out of the passenger door and felt like it might actually be right front, but left front leaning out of the driver's... when listening from the hood, sounds like it's near the fuel line, or slightly right of center somewhere on the firewall... very frustrating.

Will update if I get to checking this.

I only have a cheap P-code reader, but nothing at all and no lights... I am new to Prius diagnostic tools and haven't yet had time to grasp the current metagame of ODB readers, apps, minivci cables etc. by pouring over the forums here. Any quick recomendations for what I should grab, or a link to a thread/sticky with best current practices and info?