noise when standing still

I haven't noticed that, but then I don't spend much time in that mode. Does it sound like a fan, or something else?

Tom

 

Since you say "not in ready" I assume that you are IG-ON. You might be hearing the sound of the inverter coolant pump running. To verify, open the hood and listen to the sound of the pump (near the driver's headlight assembly). Is this the same sound?

If you left your car IG-ON for three hours, the 12V auxiliary battery may be drained to the point that your car will not start. It might be better to make the car READY if you need to work with power on that long.

 

Spending that much time in ACC or IG-ON you are in danger of draining the 12V battery. Either turn the car ON so that it can manage the battery normally as it was designed to, or leave it entirely OFF.

 

The two most noticeable underhood noises, absent any of the brake
stuff, come from the inverter coolant pump and the throttle
motor. The latter is a higher-pitched, sharper buzz, and if
you grab the spring assembly on the other side of the throttle
throat from the motor housing and try to turn it a little bit
you'll hear the timbre of that note change as the motor fights
your attempt to move it.
.
_H*

 

Two of us were out running errands today. At one point I was alone in the car and the errand was to be short, so I kept the Prius, 2008, in ON-Ready mode because I read here that doing so would obviate, or greatly diminish the start-up low MPG. Scan Gauge engine coolant temp 175 deg F.

All the while there was a faint, low level hum, coming apparently from low down on the left, under the dash. It wasn't very loud, and it didn't sound like anything was in a state of distress. My foot was off the brake, all lights off, stereo off. The state of the air co; outisde temp 46 deg F, set temp 65 deg F. I had been driving around on recirc air with fan off, air co off.

So, I tried some variations of the basic electrical conditions to see what would happen:
Power down; no humming.
Foot off the brake, push Power button; no humming.
Foot off brake, push power button second time, Accessory mode; humming
Foot on brake, push Power button, On-Ready mode; humming.

Because of the airbag/seat belt sensor in the drivers seat, one or more of the CPUs "knew" that I was in the car. I haven't the faintest idea what difference this would make.

Next time I have the right conditions I'll have to run the above test:
sitting in the passenger seat,
in the back seat, and
no one in the car (driver's window open to listen for hum)
and see if the outcomes are different.

 

My test period ran about 20 min.

I found the noise not unpleasant; as a matter of fact I felt like I had a trusted retriever at my feet eager to do my bidding.

Nonetheless, I really would like to know what piece of equipment was running.

The noise shouts a clear

WARNING: If you are to stay in the car for any length of time, you should either be fully shut down or in the On-Ready mode. Otherwise you stand a very good to certain chance that you will run down the weak-sister 12v battery, and then BIG TROUBLE if you're not prepared.