I really need to figure out how to methodically troubleshoot a whine/hum

For starters I am very disorganized. I am diagnosed with ADHD & unless I have a guide I find myself all over the place. As of right now, as far as I know, this whine'hum is not causing any major problems. However, I am aware that it could be indicative of a something that could end up being a mess. This whine/hum has been going on for " a while". I think that instead of trying this thing & that thing, maybe this methodical going through would be more productive given my propensity towards "shiny objects".

So 1st question is, if I am not getting a check engine light, does that mean everything on the code list is not a problem? This has confused me for quite some time as I have wanted to go through the EVAP, yet wouldn't I throw a code if that were an issue? Plus it's a little confusing. It seems as if it's electrical, yet there's vacuum instructions (or some such, been a while since I looked at them.) On the other hand I have a slight exhaust leak at the catalytic converter flange. Why isn't that throwing a code when I have not kept up on the patch job?

Also the electrical stuff is still baffling to me, as well as how to check for air leaks. Not enough hands on yet. I think I have found something like some kind of light (infrared?) & then it states it's for a/c. I have the link to the electrical posted on here, but some of it is ? Like where is a good place to start with using it to engine troubleshoot.

I have a Haynes, which is great for some things, but not so much for complete how to's & of course finding an official Tacoma manual online is not happening.

I also have a stethoscope. Picked it up on a whim. Not sure if it'll do me any good?
Oh, & basic stuff is taken care of. Plugs, fluid checks/changes, etc.

Any guides/advice would be great to help keep me on track. I have been so focused mostly on suspension stuff, it'd be good to thoroughly get to know my truck after all this time.

 

If it ain't broke, don't fix it.

Any idea where the whine/hum is coming from? Do you have a supercharger on your truck?

 

I added comments in the quote above.

Your ADHD is just an unsharpened tool, until you focus that energy.

If it whines, it spins. Like @Jon64l asked, where is the noise originating? Engine? Or another component when only heard during driving?

If your catalytic sensor is before the exhaust flange which leaks, then the sensor is upstream and won't notice the problem.

 

for starters need year......model.......mileage.........if bought used

ALL important info indicative the condition of vehicle

always work on 1 thing at a time
not sure if Ur whine has ANYthing to do with air leaks

many vehicles to daye will throw w ‘ check Engine Light ‘ if the gas cap aint tight
not the end of the world

sometimes its critical..............sometimes NOT

in Ur case U have a high case of ‘ What If’d ‘ chasing U around
in that case its best to see matters are correct............mostly left stock

 

To check for Air leaks in Vacuum hoses spray Carburetor cleaner or Starting fluid on hoses while engine idles. RPMs will increase if hose is leaking.
Regarding the CEL
Professionals rely heavily on diagnostics using OBD2 scanners that plug in under dash and in engine bay.
An OBD2 engine ready test will show green when each system test is completed and functional.
Red is indicated as incomplete test and becomes a stored code.
Two stored codes for one system turns CEL on and gives the code # to indicate which system has a
malfunction.
This way the computer tests twice before throwing a code and turning on the CEL.
I recommend Autel 539b OBD2 tool as it also functions as multimeter and battery load tester as well as live and freeze frame performance data.
Or just trust that if the CEL lights with key on and goes out with engine running all is good.
Now to the whir/humming.
Three belts spinning pulleys, pumps and compressor plus a fan and it's clutch are noisy but shouldn't screech, howl, tap, click, clunk or yadda yadda yadda. A whirring at start up is normal.