Mine has whined from Day 1 whenever MG2 is either driving the car or performing regen braking. The sound is easily drowned out by ICE noise, wind noise, road noise, vent fans, stereo, flatulent passengers, etc. so it's not surprising that you don't notice it all the time, but it is always there. The pitch and level changes depending on the electrical load. Easiest way to demo is with windows down on a windless day coasting to a stop. Change the pressure on the brake pedal with varying amounts of light force (vary the amount of regen braking) and you will hear the whine change.
The noise can also be heard on acceleration at low speed, but it's a bit trickier to notice. Again windows down works best, if you pull off a full EV start from stop then it's quite noticeable. Also, if you do an easy start from stop right after system start with a cold ICE, the car will often prefer to let the ICE idle and accelerate mostly from battery. The idling engine will be quiet enough to allow you to hear the whine. Anytime the ICE is producing power, it will easily drown out the whine and normal engine noise is all you will hear. That's why it's mostly noticeable during braking, because the ICE isn't producing power.
This noise is one of my favorite features of this car, I will often shut off the radio and vent fans just to hear it.

 

If and when you get married you'll develop "selective hearing". It's a defense mechanism all married guys develop

 

childers — There are two sources for the whine: (a) magnetostrictive noise coming from the motor-generators and caused by the heavy currents flowing in the coils, and (b) acoustic noise from the inverter switching transistors. The heavier the current, the greater the noise. The motor drive system uses pulse-width modulation, and the transistor switching frequency is changed as a function of the motors' speed, probably to prevent switching losses in the transistors from increasing as the motors' speed increases, and also to reduce the audibility of the noise generated. As I recall, the switching frequency varies in the range of 1.25 - 10 kHz. The windshield is designed to absorb well in the frequency range where the human ear is most sensitive (~3 kHz). The whine is most audible with the windows open, and when the ICE's noise is lowest. If this has truly increased over time (I haven't found this to be the case), the likeliest cause in my opinion would be loose laminations or coils in the motor-generators. Toyota carefully controls the MG currents to keep things within design limits, and so it's unlikely that you have caused any damage to your TCH.

Stan

 

I have to agree that with Droid13 - I have heard this noise from Day 1, even with the windows up. I haven't noticed any increase over 11k miles.

 

Here, check this nifty link out which explains what the PSD is actually doing:

http://eahart.com/prius/psd/

Other than the fact this gizmo is load o' fun to play with, it also demonstrates that if the ICE is running at an idle and the car is stopped, the wee-little MG1 is spinning around 4000 RPM, which would explain the whine I hear in my garage at startup. I'd also agree with Droid13: it's a really cool sound. You'll also see why the ICE must come on (at least spin) when the car is doing 42 MPH. Does it actually have anything to do with the whine folks are discussing? Maybe. (Yes, I know the link goes to a Prius PSD, but fundementally, the Prius and TCH are similar.)

 

I am impressed with your knowledge on this issue Stan.

 

Stan is a smart one. I was waiting for him to respond.

 

You embarrass me, guys. Anyway, I was basically remembering correctly. The more detailed answer is that:

• MG1 uses a switching frequency of 1.25, 2.5, 5, or 10 kHz
• MG2 uses a switching frequency of 1.25, 2.5, or 5 kHz (I don't think it ever spins as fast as MG1)
• the dc-to-dc converter uses a switching frequency of 5 or 10 kHz

You'll find this information (and much more!) in the attached pages HV-42to49.pdf from the Repair Manual.

Stan

 

Jeez Stan, I swear you must have that memorized! I've looked at it and don't like the way it documents most repairs. I have a hard time finding specs on things.

 

mikieboyblue — No, my memory isn't that good! Whenever I find something I consider interesting, I print out those Manual pages. The problem then is to look through my collection of printouts to see if I can locate the item that I recalled seeing before! (Of course, you first have to browse through the Manual fairly thoroughly, so that you know what's in it.)

Stan