Strange High-Pitched Buzzing When Motor is Off

It's normal for the car to have a sound when it's on.

But I would be more concerned about the low oil

 

Was the A/C on? The A/C makes a buzzing noise.

 

Well the Prius is somewhat known to burn some oil in between oil changes. You would have to add as needed. If the previous owner neglects to add oil and let it burn down to nothing, then you'll have some issues later.

 

Does it sound like this ? Possibly the water pump on its way out. Mine was making this noise right before I got a check engine light for a water pump code. The pump seized up.

 

You got a code for the pump? Man, you are lucky. My 2010 never threw a code, and the first time I found out I had a water pump issue was when it overheated on my wife and went into safety mode.

But yes, OP that is the water pump you are hearing. I will run even when the ICE is off because it's electric. A new pump will not whine that loudly.

 

While searching for other threads for posts showing signs of a bad water pump, I came across this video...
Sounds almost like mines, but with more scraping:

I just bought this as NEW from an online dealership near Boston, and have now just read their return policy and it looks like I am out of $200
Car ran fine after I performed an engine swap, and around 180 miles in, I started to get overheating issues and after many burps, bleeds and vacuum tests of my coolant system, it's starting to look like it's this pump!

 

That last video is clearly a pump sound, but the video from Joele3 is just the normal sound made by the throttle body. The throttle valve is positioned by a an electric motor being sent controlled pulses by the ECM. For whatever reason, the ECM keeps sending positioning pulses even when the engine is stopped. The sound in Joele3's video is just the sound produced by that pulse train and the magnets in the throttle motor.

You possibly won't take my word for it until you take a mechanics' stethoscope (they're cheap) and touch it to the throttle body directly. After that, you won't need any convincing. Or unplug the throttle motor and hear the sound stop (you'll get a trouble code though). It's funny what a variety of other things people end up guessing that sound is.

A fun thing about the throttle body buzz is that the throttle body has coolant piped through it, and water is a strong sound conductor, so you can pick up the same sound lots of places around the engine compartment. There's a large coolant pipe down the middle of the engine compartment that also gives off some of the sound (probably why some people guess it comes from the inverter). But if you chase it down you will find the throttle motor is the source.

 

Interesting, yes unclipped throttle and sound went away. Does coolant come from invertor pump coolant or other? Interesting that my 2004 sound came after pump changed, but also had throttle cleaning, so not sure which activated. bothersome. IS it correctable?

 

The throttle body is part of the engine coolant circuit, not the inverter coolant circuit. (Note that the engine coolant circuit in a Gen 2 goes kind of everywhere, even to the thermos out under the left fender, so the sound gets carried kind of everywhere too).

Because it's a normal sound produced by the normal throttle body doing what it normally does, I'm not sure how "correctable" it can be. It's possible it might get more noticeable as the TB bearings age, or something (I'm totally guessing here); if you replaced it you might find a replacement to be quieter. Or you might not. Or the replacement might be louder and you'd be really disappointed. It would all have to be judged against how much you want to fuss over a sound that isn't abnormal.

 

Update:

So I've been planning to taking a beat to update everyone what happened after this video, but just thinking about it just gives me a headache. So long story short for now, I swapped out the Gen4 Water Pump with another NEW OEM one. After doing my best to bleed it, the new one made the same exact noise and I was still having creeping Overheating issues.
I spent like over 4 hours with the car outside, doing another bleed- jacking the car up and down and letting the coolant overflow out from the reservoir in its position and elevated from a bungie..jacking it up and down, forcing coolant into the purge valve..I tried it all to no success.

I threw in the towel and txt'd a buddy who used to be a Toyota Master Tech and told him everything I've done in the last few months with this car- which I was hoping to get the swap running and impress him with what I've done, but this became a consult instead. He then told me his experiences in the past in dealing with these Gen3's years ago while he then worked for Toyota, and the lengths the techs had to go through just to bleed the coolant systems in these cars. I asked him to go over everything involved in the swap that I performed, like checking the engine, the water pump, thermostat, egr, cooling lines etc. and assured him I would pay his rate for this inspection as I wanted to learn what from this experience on what went wrong.

So he had the car for around 2 weeks, checking over the engine, and everything else related to my swap. He did note that the water pump was working as it should (as seen through techstream) and that the noise we heard on the video may very well have been due to the air in the system causing that weird howling noise. He also couldn't find anything much happening with the 2018 engine itself, but was wondering about the crank and its communication with the 2010 ECU and would ask some of his other former colleagues how different- if any, are they from the 2010 engine...

After another week of testing and driving it, he just couldn't immediately see why there was still air in the system. He did advise he didn't find much wrong with the swap like the coolant lines, or wiring. It was at this point I gave up and offered to sell the car to him. I was just done with this turd. I lost all confidence with this thing to ever run 'normal' and not slowly creep up and overheat and leave me stranded somewhere.

He said he would continue playing around with it to see if he could find out what was causing this and let me know so I could learn from this, but I am just so over this.

I'm now back to DD'ing the F now. Just gotta remember to keep the speeds down!

I kinda did have some fun and took on the challenge of doing a job like this and learning some new skills along the way.