The Engine is Louder After Oil Change?

Sorry; worrying about it isn't going to do anything - any damage done, has been done. You should've done something 5K miles ago. I believe you have a 5 year 60K mile warranty powertrain. Arguing about how they damaged your engine between 5K-10K oil changes will simply make you sound like a nut job...... Someone that'll drive their new car making strange noises for 5K+ miles?

Check your receipts. What oil weights did they use on those oil changes?

 

TL ; DR

^ That.

So....
I do not and HAVE NOT allowed a dealership to change the oil in any of the last 8 vehicles that I have owned.
But?
I get it.
Many people do not, or can not change their own oil.
Heck...I'm surprised that some of our '52 laboratories of Democracy' actually ALLOW people do DIY their oil changes without licensing renewable certification and insurance.
However...
(Comma!!!)
It's still your car.
You can STILL take ownership of the ownership experience.
What was the oil level before and after the 5k 'service?'
What is it now?
Did you mark the filter in any way?? - yeah, it's harder on a Prius to be sure but doable.
What other 5k checks were supposed to be done - and WERE THEY?
I can think of many things that would cause the noise - including nothing at all - but a few more breadcrumbs might rule out some of the more obvious ones:
Wrong oil used. (**)
Oil cap improperly replaced.
Insufficient sump volume.
Superfluous sump volume.
The fact that the dealership might HAVE ACTUALLY DONE a 5k check that included a tire rotation that increased road noise that presents as engine noise. Again - not likely but possible!


Personally?
I would put the giveacrap switch in the "do not" position and get on with my life.
There IS value in maintaining a 'closed hood' maintenance philosophy.
Heck.....I sometimes wish I could afford to do it myself!!!
(Meaning NOT do it myself! )

JUST Remember that one of those benefits is NOT listening to every creak, rattle and groan in your engine compartment like a new first time parent cracking the door to the nursery every hour or so to see of the baby is still breathing.

Buying a new car every 6 years (or 100,000 miles) and having it "dealer maintained" is a very VERY convenient way to own a car - and it makes all kinds of sense in some 'life coachy' sort of way....I s'pose.
UNLESS......
You're going to be keeping the car for more than it's design service life of about 10 years or 250,000 miles.
You are retired or have a realistically funded retirement plan.
You have already made launch plans with funding for your kids - or you just don't like them very much.
You are extraordinarily wealthy or a person of only average means.
You are extraordinarily healthy or very unhealthy.
You DEPEND on your car for various reasons instead of just using it for 'personal transportation.'

BEST OF LUCK with the car!


(**) From the Googles: SAE 0W-8 oil is factory-specified for the 5th generation Toyota Prius (2023–2026 models) equipped with the M20A-FXS engine. However, regional discrepancy exists: Toyota's North American manuals initially recommended 0W-16 for these years, while the Japanese and other global markets have specified 0W-8 since day one

 

Did you check oil level on the dipstick after that first oil change?

 

I'm pretty sure you have a spin-on filter. A misplaced O-ring on a cartridge filter or misaligned center tube is what your describing above and an ineffective oil filtering system - in that configuration. Again; I'm pretty sure you've got a spin-on oil filter NOT a canister/cartridge style.

 

I think this is a wise move.

For other folks, if you can't do your own oil changes, no worries, then find a local highly trusted and competent local mechanic and go there for your oil changes. Do NOT go to a dealer or jiffy lube type place. Because that is a recipe for disaster.

(I don't love to be under my car either, but installing a fumoto valve has made oil changes so easy and so cheap, l can't justify going to a shop for those.)

 

Having basic maintenance done at a dealership "can" be uneventful, IF you're firm with them regarding the extras they tend to push, and if they're one of the more competent dealerships. Our son just had a cylinder head replacement at a nearby Mazda dealership, next door to our go-to Toyota dealership, both ostensibly part of the same company. Ended up going well, no problems, didn't cost him a cent. Apart from about a month of car rentals while Mazda Canada and the dealership hemmed and hawed...

Bad stuff "can happen", at dealerships or independent garages. And if you're capable of doing your own basics, and have the time, it IS prudent to do so, keep a log and all receipts; you're NOT compromising your warranty, or your eligibility for recalls, TSB work. At least I hope not.