Sudden loud noise from exhaust/engine

Have you looked underneath to see if the catalytic converter is still there?

Maybe somebody whose unemployment ran out decided to sell it.

 

Did you look under the car to make sure someone didn't steal your catalytic converter? It's an epidemic right now... Happening all over the map because cats on Gen2 Prius can be stolen in less than 60 seconds and are worth more than a thousand dollars.

If that's not the problem, I suspect your cat is clogged and you blew out the flange gasket.

"Tuesday morning’s chase was Sonoma County’s second high-speed police pursuit of suspected catalytic converter thieves in one week. The county has seen a remarkable spate of over 100 stolen catalytic converters in recent weeks — usually from Prius models. Petaluma police had received a report from a nearby neighborhood of vehicle tampering by two men in a small, dark vehicle, McGreevy said. When officers spotted that car and tried to stop it, the vehicle sped off at such a high speed — at least 90 mph, police said — that pursuit was quickly terminated. Moments later, the driver lost control of the car, careening across the oncoming lane and into that tree, 150 yards south of the St. Vincent de Paul Church. In the Honda, police found a reciprocating saw and at least two catalytic converters the men were suspected of cutting from cars." https://www.pressdemocrat.com/article/news/thieves-steal-over-100-catalytic-converters-from-sonoma-county-cars/

 

Usually you see wires from the 02 sensor hanging down, as well as metal shaving on the ground after a theft. And if cat is still there it should be visible as near the lowest point of the car. So if you lay down on the ground and look under your car and don't see it, then it's been stolen.

If it's just a blown flange gasket, at least in my experience, you'd see exhaust coming up from behind the engine inside the engine compartment.

 

Here's a pic of the underside of a Gen-2 like yours. The top of the pic is the front of the car, the bottom is the rear.

 

If you can't jack it up safely to get under it, tape your phone to a broom handle and turn on the video camera. In fact, just do that anyway. It's faster and easier. You'll most likely capture video of a big empty area where @tvpierce shows the cats.

 

Can you circle the points where the bad guys cut to remove the cc?

 

Not strange at all.
Everything in the world works just fine......up to the second that it fails.
Exhaust parts expand when hot and contract when cold.
It appears that yours opened up a hole as it was contracting.

You need to get the exhaust system inspected.
In addition to the noise, it might be letting exhaust fumes into the car.

 

... or the second somebody steals it. I'm waiting to see just how big of a 'hole' is shown when the OP sticks a phone on a broom handle.

I once paid a tranny shop to do some work I felt I didn't have time to do myself, and when they reinstalled a skid plate under the transfer case, they reinstalled it backwards. It had a lip on one edge, and when installed the wrong way 'round, the lip was right under the muffler, and meant that from then on, every time I accelerated and the engine twisted in the mounts, the muffler got pressed down on that lip. It took a little less than a year for that flexing to break the pipe right off at the catalyst, on my way home from a Boston trip, and I had to live with the straight-pipe sound through about the width of three states.

 

Go you tube and look up

Prius stolen

lots of info there. Many people who live in non carb states have been selling there cats g2 cats there worth a lot of money.
Got $1350 for mine.

 

Also in Arcadia, they got mine on Friday. See

Just joined the stolen cat club | PriusChat

Report it to the police, file a claim, and then get in line for a replacement at one of the Toyota dealerships or independent shop. The line forms because so many of these have been stolen the needed components are back ordered at the Toyota distribution warehouse.

 

near the exact center of the pic between the second cat and resonator is where the back cut is done. The front cut is not in this pic but would be above the top of the photo in front of the first cat. Though some thieves realize it's quieter to not do the front cut, but to unbolt the two bolts that attach cat to end of exhaust header.

 

That is what they did to mine. One of the bolts was on the ground under the car.

 

And they chop and damage the 02 sensor harness too.

Oem cats are back ordered due to the huge demand.

If you own a g2 cat and it’s healthy and has not thrown a emissions code and you live in a non carb state sell your cat. I bought a replacement off Amazon for $129. That works great. At the muffler shop labor to remove my cat and install the Amazon cat was $100 cash quick and easy and all welded up,
I painted my Amazon cat bright orange with header paint.

after that labor and eBay fee I cleared $1000 for about 20 minutes of work which was painting my new cat and driving to the muffler shop.

Bidding was crazy like 40 bidders.

car runs better too. Sell your cat before it gets clipped. I’m hoping the thieves see the orange paint on mine and realize it’s not the good oem cat and split
Plus the after market cat pile is way bigger pipe so a offset collar was installed very common for a muffler shop so there’s a big adapter welded where they usually cut so that should make them look at the cat and hopefully not chop my car up.