Pumping/growling noise & vibration- driver's side front left floor

The only device of consequence in that area is the brake abs unit. If it has sprung a leak it will turn on the brake vacuum assist motor constantly which I am sure you have heard a million times it sounds like a rattlesnake. You can make that pump come on by pumping the brakes a few times. If its running constantly that means the ABS unit is leaking. That usually always throws a Master Caution Alarm on the dash though and the brakes feel really bad. I hope its not that is its expensive but it not throwing any dash alarms tells me it may be something simpler. But the fact that you can feel it on the floorboard has me worried.
The car is very good about throwing alarms on the dash when it is not happy. Hope it does not throw a big red explanation mark on the dash.
Have never heard this before.

What does son say any problems he encountered?

 

Does your son have the tools and experience to change the engine coolant? If he didn't bleed the system correctly, and it's quite difficult to do so, air in the system will cause a pump near your left foot to cavitate, but only on cold start up and shutdown, not constantly like you describe. Still, you want to keep checking the radiator coolant level for a week or so. And make sure you cabin heat works okay. If you can hear gurgling in the dashboard, that's air in the system.. If it needs to be bled, there are threads on the topic on this site, and Youtube videos. Keep a close eye on that--low coolant will damage the engine.

 

Ah thats a good one Andrew I forgot about the CHRS pump. I foolishly the first time I tried replacing the engine coolant dumped the whole thing....the rad...the engine...and then spent hours trying to get the air out and I had a highlift evac. That's when I discovered the joy of the CHRS pump & storage bottle.
Never going near that again.
I have found that if you dump just the rad a few times over a month it will do a real good job of updating the engine coolant and not invoke dreaded airlock. The engine is pretty easy on the coolant.

Conversely the Inverter huge cross section of aluminum is very hard on the Inverter coolant. That fluid gets contaminated pretty quick when on the original fluid during Inverter break in. But the changes after that initial break in have looked real good.

Just like the trans.The original fluid in the trans takes a beating during break in but afte that it looks pretty nice. I change the Trans and Invert coolant every 35K....now only have to do 50K as the last 35k looked real good on both.

 

It may be the inverter pump then, though that kind of noise is unusual. The inverter pump is right behind the left headlight.

There are two radiator systems on the Prius, one for the engine and one for the hybrid inverter. Before you drive the car again, check the fluid level in the translucent reservoir near the firewall, towards the driver's side. Remove the cap and look inside with a light. If you can see the reddish coolant, turn the ignition on/engine off by pushing the start button twice with your foot off the brake. You should be able to see a small flow in the coolant, and hear a very slight hum from the nearby pump, much like an aquarium pump.

If there are any problems with this system, don't drive the car.

 

Bad news, the inverter pump could be fried, thus not making noise.

Reset the car by plugging the 12v negative for a minute. If your lights return, then you would need to check the codes

 

There's an air bleeding process that should be performed when inverter coolant is drained (see Youtube). The system, though full of coolant, may be air locked. If you don't see the coolant flow and hear the pump hum as mentioned in post #6, the system is broken and don't drive the car.

 

It never occurred to me the Inverter coolant pump was so unhappy you could feel it in the car. Surprised it didn't take out its fuse. Never heard this before 10 years on this forum.

The fact that it was running dry mostly likely damaged the pump exactly like JC said. This pump is vital to the car and the car will die if the pump fails as the Inverter will overheat so badly it shuts itself off. It also overheats the transmission as it cools that also.You could damage the Inverter. This pump is not to be messed with in a G2 Prius. Its not expensive to replace and I would get it replaced asap and the coolant properly installed and bled.

 

You have the wrong fluid in it. It requires Toyota SLLC. And the pump is no wheres near your foot. Its behind the drivers side headlight.

 

Yep, you have another project. Drain whatever you put in from the parts store, as soon as possible, and refill with the right stuff ($40 from Toyota). And learn how to bleed it properly, which requires a couple of small wrenches and a short length of tubing.

And you'd better get a new pump in while it's drained. There's no way the pump was not harmed by running dry. This is one of more important things you can do for the reliability and long term health of your car.

You may want to post what fluid you put in, if you want feedback on that. Hopefully it's not too harmful to the aluminum inverter, the transaxle, or the radiator. Two of those are very expensive parts.