Hi guys! I'm a Newby, after some advice

Any warning lights? These cars have a know issue with exhaust gas recirculation (EGR) valve getting clogged, which leads to blown head gasket. Hopefully that's not your problem, but your symptoms at first glance point to this problem with early model Gen3.

If that problem is confirmed, your options are to replace the head gasket or replace the whole engine with a low mileage used one...

 

Yeah best place for this would be third gen maintenance forum. I think this forum is purely for introductions? I’ll report and mods may move it.

Does sound like the tiresomely regular head gasket failing. How many miles, what year, and has the Exhaust Gas Recirculation and Intake Manifold ever been cleaned?

I’d speculate there’s a correlation but that would bring someone out of the woodwork. So I won’t...

More info:

Bad Flywheel | PriusChat

 

Gasoline engines can misfire for all kinds of run-of-the-mill reasons, and in a Prius any run-of-the-mill reason for the engine to misfire can give you a racket like that.

Here's an old story of a Prius being sold for scrap price because of that kind of noise, and the cause turning out to be one bad spark plug. I've mentioned it before in other threads, like this one where the cause was one bad coil.

On PriusChat you can always get someone to tell you your head gasket's shot and the engine's a goner, because Halloween's just around the corner, but if that's the case you'll find out in the course of working up the misfire anyway, and if that isn't what's causing the misfiring then you'll find out what is.

 

If it clears after a minute or so and then runs fine, its a head gasket. It will not throw a code if it clears up quickly. When it gets worse, the coolant level will slowly drop. White smoke is the last symptom. By then it will be showing misfire codes. People usually verify or replace spark plugs, coils and injectors before total acceptance. 2010-2014 Prius engines are notorious for this. And we are a long way from Halloween.

 

I've heard of startup rattles, clearing within a matter of seconds of starting. And I've heard of a sustained misfire that just keeps rattling and rattling. The OP's video is 21 seconds long, certainly longer than any 'startup' rattle I've heard, and seems pretty much sustained, though of course if we introduce a new category "rattles that clear after a minute or so", then 21 seconds isn't quite enough to rule that out.

On PriusChat, Halloween is always right around the corner.