Car sounds like angle grinder

1) When you open the coolant reservoir cap does it make a sucking sound?

2) Consider cleaning / having an Exhaust Gas Recirculation (EGR) valve maintenance schedule

3) Aggressively shake your tail pipe when this noise happens to ensure it's not loose exhaust shielding

 

Could be the water pump bearing or pump idler pulley. Sort of hard to locate and confirm though. I've used the piece of broom handle to ear technique, which must be done carefully around moving parts. A precise squirt of water may also temporarily eliminate the noise. Or loosen up the water pump belt and remove and see if the sound stops. Don't run the engine very long though.

 

There are NO belts on a 2010 Prius. Nothing to snag.
Hard to tell from the video what the noise is, it almost sounds like a rattle, like something is loose.

You could use a screw drive, long one, or long socket extension, to the ear, and touch the water pump.
If it's the water pump, you'll know it instantly. You also have the inverter coolant pump, it's under the
fuze box.

What area is it coming from? Have someone start the car while you are listening close to the engine.
I would say it could also be the ac compressor, but with the cooler weather, it probably no turned on.
But check to make sure...

 

Oh, yes, sorry. I was remembering my 2008. I'll see myself out...

 

It's not that big of a deal...

 

Opening the coolant reservoir to the sound of air sucking in is a sign of lost coolant due to blown headgasket.

 

Time to check the dipstick......

...and prices on a replacement........

 

For starters that does not sound like a HG issue and people are already pointing you in the direction as if it was.

The coolant res will always make a small hiss but if it last like 3 seconds a sounds like pffttt, then you have a blown HG.

Best to check that in the morning on cold start.

I would assume like someone else said the waterpump or pully.

 

How many miles?

 

I have a 2015 Prius experiencing the same issue (same sound from your video). 151,000 miles.

**Did you ever find out what the issue was??**

 

are you losing any engine coolant?

 

Angle grinders are crazy loud. Was it ear protection level loud? I wouldn't be driving the car in those circumstances.