It's really hard to say what exactly is going on from what was typed, at least for me.
That's the problem with these situations, it's very subjective and we have to either make assumptions which could turn out to be wrong, or else ask a bunch of questions which if worded incorrectly can sometimes come across as challenging or dismissing what the person is reporting.
The tricky part is that there is quite a bit of evidence in the four years that the Clarity PHEV has existed that there are a few owners out there who have at times experienced a clear issue with their car, behavior and noise and RPM's that are way beyond what would be considered normal. One of the symptoms is that it happens only occasionally, some have experienced it only a few times, weeks or months apart. And for some people it doesn't always happen with 0 EV miles, which supports the theory that it is a software issue where the system thinks the battery is fully depleted when it really has 10% or more SOC.
This owner's experience is somewhat unusual in that it sounds like it is repeatable and frequent, and also apparently only occurs when there are 0 EV miles. That would normally make me want to put it into the category of a new owner who is not used to the somewhat unpredictable engine noises that pretty much any hybrid makes at times. But in this case words like howling, struggling, and redlining make me at least consider the possibility that this is not normal behavior but one of the rare software conditions that some people have experienced.
sounds normal to me. the ICE is generating electricity that is being used by the electric motors to accelerate the car.
Unfortunately none of us know what it sounds like. You could be right that it's normal, but it requires hearing it in person to know for sure. We can't necessarily assume that he is hearing the same thing that we hear when we drive our cars.
In the past myself and others have encouraged people with this problem to get an OBD-II connected so they can tell us what RPM's they are seeing, which would give us something to compare with our cars. Or using a db sound level app on their phone, although imprecise it could provide some quantification to what they are hearing. Or an actual audio recording, even though it may not full convey what they are hearing it would at least be something. Unfortunately most people who come onto sites like this asking for advice are not usually interested in doing a bunch of diagnostic steps, which I can understand, but that further takes away any ability to understand or quantify what they are experiencing to determine whether or not it seems like normal behavior.
Adjust valves if they are noisy.
Is that even possible on modern cars? I used to adjust the valves on an old VW bus, and one time on my old Datsun using a special tool that I had to buy. Every car after that it was not a DIY procedure, nor did it seem to be necessary and was not part of normal maintenance schedules. Also noisy valves tend to make a chattering sound, and while it can cause a loss of performance, I would think the odds of a Clarity engine having valves so far out of adjustment as to cause noticeable performance issues and high RPM's seems unlikely, especially since most Clarity owner's engines don't have a lot of "miles" on them, i.e. HV miles. But that's just my guesstimate.
Engine air filter replacement
Easy to check, and not a bad idea on its own. I would be surprised though that's what is causing the high RPM's and engine noise, but you never know.