Horrible racked noise at start up

It depends on your definition of "fine". I expect @danlatu would recommend installing an oil catch can.
The cold startup rattle can eventually require the engine head gasket to be replaced or the engine to be replaced.
People have had good results installing the OCC to eliminate the knock.

 

@Mendel Leisk @bisco @Raytheeagle or one of the other more senior members would be better able to answer that.

 

I'd say turn it off asap when hearing that sound: don't prolong the agony. Restarting, the noise may be gone, at least that was my experience, the one time I've heard that.

It was also one time that'd I'd fired up the engine for only a few seconds, the day previous. It's speculated this might trigger it. @danlatu has some specific ideas as to the cause, and suggests an Oil Catch Can install, coupled with intake manifold clean out. I've done those. Here's a good thread on that:

Oil Catch Can, Eliminate that knock! | PriusChat

Also look into EGR circuit cleaning, @NutzAboutBolts has a video on that, pinned in the maintenance sub-forum:

Nutz About Bolts Prius Maintenance Videos | PriusChat

How many miles on it btw?

 

I think the easiest way is to post on Youtube, then you can link it here. I say "easy" at arms-length: I've managed it, but there was a definite learning curve for me.

 

it's fine to drive, no worries.

 

yep, that's it!

 

Funny: you just had an oil change, and in the thread you linked the Initial Poster also had just had an oil change.

There's a knowledgeable member (sorry, can't recall his name right now) who mentioned (quite a while back, 2008?) that fast oil fill after a drain may result in some oil flowing into the intake manifold. To be fair that's the first I've ever heard of that, suprising there's not more about it.

Ah, found it:

Overfilling Oil | PriusChat

And up the page, post #3, by @tochatihu

 

Wow, Youtube move over: I've got to look into that.

 

That video sounds bad btw. If it's not knocking I'd say you're fine to carry on; it seems to be an intermittent thing.

I suspect dealership will be exercise in frustration and $'s.

Yeah, look into OCC, clean intake manifold, clean EGR. The latter is a bit of an undertaking: watch the videos. Start by cleaning the EGR "pipe". There's a video on just that, and it's relatively easy section of EGR to get to, and will give you some idea judging from it's condition. I think @NutzAboutBolts recommends 120K miles for this? I did my EGR at 72K kilometers: could definitely have gone further, not badly clogged at all, but better sooner than later. We're low miles and at 7 years, time on my hands, so it was what the heck.

Also have a read through this thread, for EGR:

EGR & Intake Manifold Clean Results | PriusChat

(I get in gear on page 3.)

 

Trouble with EGR clean through dealership, they very likely would prefer to just swap parts, not clean, and the parts are expensive: $450~500 for both the valve and the cooler. A third party mechanic, willing to pull the parts and maybe you just clean them, or replace with pre-cleaned E-Bay parts, is another route. DIY, cleaning what you've got, is hands-down the cheapest, basically free, apart from the expense of a can of Brakleen and some Oxi-Clean to soak the cooler.

Tools for the complete EGR, you need the basics, a 3/8" torque wrench is good, something that can get down to 5 foot/pounds. A 1/4" torque wrench is even better. Also a E8 Torx socket (probably 1/4" drive) is mandatory for EGR cooler stud removal, and E6 if you want to remove the two throttle body studs, when doing intake manifold. A ratcheting 12 mm box wrench makes it a lot easier to remove some hard to reach nuts at back of EGR cooler.

I'd suggest to take on the check of the EGR pipe yourself, see how gummed up it is, go from there.

Some Repair Manual info, attached.