2010 engine ticking noise, need ideas

So within the last few months I've noticed that my engine now ticks.

2010 prius
225,000km
No coolant or oil loss (knock on wood)
EGR / intake system cleaned
New plugs, pcv
Occ installed off pcv
CVT fluid changed
Mobile1 0w20 oil

I've owned the car a couple years now and never noticed it before until recently. At my last oil change I put in some royal purple 0w20 instead of my normal mobil1 and an oil additive to help rejuvenate the engine (snake oil science)

With the pandemic the car has gone from driving 1000km a month commuting to maybe 25-30km a week of errand running, short trips. I recharged the A.C. and I sound deadened the interior recently which is when I noticed the ticking.

Symptoms:
-Engine starts normally, no rough starting ever.
-After a couple seconds the engine Will start to tick, tick matches rpm.
-When I'm parked and rev the engine slightly the ticking will quiet and it sounds normal, when it goes back to idle it starts ticking again
-while driving it will tick under load or acceleration, more noticeable the harder I accelerate, still matches rpm.
-with the windows closed, and driving I can barely hear it if the radio is off. Windows open I can hear it when the sound bounces off the environment.
-if I take it for a longer drive and get the engine good and warm, I feel like it's less noticeable.

Additional info:
-I changed the royal purple oil out for mobile1 at 1000km and added some liqui moly hydraulic lifter additive as well as liquid moly jectron fuel system cleaner. I've driven it about 200km since doing the above and haven't noticed any major change in the tick.
-The oil I pulled was clean, no signs of contamination and the coolant levels haven't budged.
-Fuel economy hasn't changed, still sitting around 5.0l/km.
-No dtc's or performance changes.

I've read that the 1.8l has hydraulic lifters and shouldn't normally tick, they're also a pain to adjust/replace.

I also don't know if it's my valvetrain or my injectors because both can be noisy.

Is there anything easy I can do to try and further troubleshoot the noise? Like pulling the Valve cover and checking for play or running higher octane fuel or replacing my vvt solenoid or knock sensors?

Or
Should I even bother pursuing this further and just accept that my car ticks now?

Any gen3 gurus have wisdom they're willing to share?

I'm not afraid to get dirty and have plenty of mechanical acumen and tooling to resolve problems that don't absolutely require a professional touch.

 

I haven't localized it to the top or bottom. I don't have a stethoscope or have I ever used one so even if i did use a method to isolate the noise i'm not confident enough to know what I was hearing.

I've only theoretically isolated it based of dohc head design.

When i said that it matched the rpm that was a poor categorization of the symptom. I think a better way would be to say that the ticking follows the rpm in a linear. 1 tick per rpm/2 which would theoretically indicate a problem with a lifter.

That being said if we were to assume that I did have a bad valve adjuster.

1) it's quite an involves process to access them for replacement, can they be cleaned or replaced without removing the cam?

2) if I'm going so far as to remove a cam I may as well go further and replace all the lifters, headgasket and water pump and leak check all the valves because it's only a few more bolts at that point. I'm not super keen on doing that unless I need to.

3) other than being noisy, is there any real harm in just leaving it and trying to clean the lifters by running some engine flush through or other such chemicals?

4) can I pull the Valve cover and try cleaning the lifter pathways with a bit of brake cleaner and some dental picks?

5) taking it to a shop is kinda out of the question because shop rate for a valve inspection is 8hrs which is a huge coat with parts.

Should I just accept it ticks will any real harm come to the engine with a noisy Lifter?

 

I loaded a metrognome set to 500 bpm and it sounds really close to the engine at idle. This is an approximation by ear.

I don't want to replace everything but if I need to remove the cam, then I need to remove the timing cover to disconnect it from the chain sprocket. So if the cam is removed, the extra cost to so all the lifters would be justified if it means I never have to remove the cams again for the life of the vehicle.

I was exaggerating when I said a few more bolts, I've got 3 young kids so if I'm tearing my engine apart it's going to take a lot of time to do. To me it's less overall time to go all the way to the head gasket if I've got the timing cover off then to just do a valve adjuster and then have to do the whole process again another time for something else. It's really more of a personal assessment of how much time I can devote to tearing engines apart.

 

I would likely go so far as to try a stethoscope to approximate the tick and remove the Valve cover to visually inspect the valvetrain for signs of obstruction or damage as its involved but could be done in a couple hours. Beyond that it's a major time investment if I couldn't remove the cam without removing the timing cover, wirelocking or otherwise.

This would leave me with the option of living with it until something else goes and trying various other cleaning methods like engine flushes or seafoam or different grade oils to try and dampen the noise.

Is a noisy lifter worth all the hassle of fixing or can I leave it and not worry about it? I've read about all kinds of engines that have noisy lifters and it's just universally accepted as a nuisance that comes with high mileage engines.

Thanks for your input and help Chapmanf. I do appreciate it,

 

I've come to an interesting bit of progress on my ticking problem.

After throwing some money and a couple days of wrenching at this problem, I've discovered that i may not even have a lifter issue at all.

So after the world's most expensive diy oil change.
Royal purple 0w20 (1000km)
(Fram ultra synth filter)
Mobil1 0w20 (300km)
Liqui moly hydraulic lifter additive (200km)
Liqui moly engine flush
Motomaster 0w20 (flush out engine)
New fram ultra synth filter
Liqui moly 0w20

I've discovered that i have a small hole in or around my cyl#2 exhaust manifold. I noticed it while cleaning off my timing cover seepage during my oil change party.

It's not definitive but I have to fix it before I can further diagnose this issue. It would make sense as the tick would get louder and quieter depending on the load and rpm of the engine. It is possibly not a tick at all but a leaky exhaust manifold on 1 cylinder.

 

Yes. There was a pinhole leak about 1/8" in the #4 cylinder exhaust manifold pipe. Once I got it changed out the sound went away. It took 3 different exhaust flanges to get the manifold to seal properly to the catalytic converter but the sound is gone