High pitched inverter noise & electrical sound

Your first recording does sound like it's from the inverter, especially with the pattern you've noticed of more loud when sending more current to the battery.

The second recording, I bet you will find is the sound of the throttle body. A mechanics' stethoscope is a cheap tool to buy (and if you don't have one, you can even use a long screwdriver or a stick, pressing one end to your ear and touching the other to different things to check the sound, though a stethoscope you buy works even better). We have a sort of common PriusChat routine where people hear that sound, and can't be persuaded it's the throttle body, until they get a stethoscope and check for themselves.

Here is a post that covers why the throttle body makes a sound like that.

It's a normal sound, but there can be a lot of reasons a person might notice it more than before. Being hyper aware is one possibility. Also, all that stuff got unbolted and reattached as part of the head gasket job, and if some bolts are tightened differently or a rubber gasket's a little more squashed, that can change the way sounds carry.

A sound made by the inverter has a similar explanation; transistors are used in there to quickly switch electrical currents on and off, at frequencies a human can hear, and the corresponding magnetic fields can make some stuff vibrate slightly at those same frequencies, giving sound. The fields are stronger when the currents are higher, explaining the louder-when-charging part. Again, it's possible you're newly hyper aware, or that some of the work in the engine compartment has left the sounds traveling a little differently. Nothing about it worries me.

 

First sounds more like valve clatter. Second is definitely a brushless stepping motor being driven at audio frequencies.

 

What’s the miles on it?

Was the EGR system, including intake manifold, thoroughly cleaned?

 

The throttle motor is a two-wire DC motor ... not enough wires to be a stepper. It goes one way when given + − and the other way when given − + (and when not given any electrical power one way or the other, a spring sends the throttle back to a fail-safe, very slightly open position).

Whether it is brush-commutated or brushless, I don't know for sure; I haven't taken one that far apart, and nothing in the New Car Features manual seems to make any point of saying it's brushless.

But the basic point holds: send driving current to any kind of motor at audible frequencies, and you're going to get some audible sound. A stethoscope will make it easy to confirm the throttle motor is the source.

 

Not really. My 2 cents: you need to get both the EGR components and the intake manifold (which has the final leg EGR passageways) cleaned, ASAP, if you don't want another blown head gasket.

Professionals that'll do this, effectively/thoroughly, and for a decent price, are few and far between. Tampa Hybrids (Florida) and Hybrid Pit Stop (California) are the two mainstays. Dealerships are a joke, will only replace parts, and the parts cost alone is about a grand.

DIY is the way to go if possible. Or connect with someone who knows the story, and is willing to help out. See first two links in my signature for info (on a phone turn it landscape to see signature).

Ideally this should be done about every 50K miles, due to the 3rd gen EGR system's propensity to accumulate carbon deposits.

 

Better save up a bunch of extra $$$ for all of the bad stuff that's going to happen soon....