A1398 2015 - wearisome fan whine

[Intenditore]

I've got A1398 2015 (2.8, R9 370X, High Sierra) which I was dreaming of for years! I bought it for silence as Apple values it much - and got something pretty different.

First of all - paste is fresh (MX-4), fans are clean, SMC and NVRAM are reset. I undervolted with Volta (-60mv), turned off Turboboost and limited the TDP to 35 watts (despite the scorny filings).
It made it somehow better (by the price of -20% of performance, from ~580CB points it dropped to ~500 while 640 is normal for new machine), cause usual Firefox browsing could kick the fans to ~30% with no effort, now it's much better. But weird.

A few runs of Cinbench CPU, temps are about 80C - silent. Only on the third run they start to rise to ~20-30% and usually stay there. Than two runs on the GPU and despite temperature is about 70C it kicks the fans right away to 40%! I stop it and about a minute more the fans are working hard, even when it's 60C already.

A simple editing in C1. Just adjusting curves - oh no, it goes full blast for another minute with no reason! No higher than 70C in peak, about 63 usually meanwhile.

I tried TG Pro, it allows to downspin the fans. I was happy, until I a MASSIVE THROTTLING became apparent, the second run of Cinebench CPU

I'm exhausted. I value quietness much and this whine makes me very nervous. How can I manage it? Help me please...

(sorry for foreign language on the screenshots, I translated what's needed)

 

[Intenditore]

Nobody can suggest anything?

I noticed most of all times it's happening when I do anything with AMD graphics. I start Cinema 4D, and after a half of a minute of very light 3d work, it may be even a simple cube in viewport and nothing else it starts to rattle disgustingly. And when I stop doing anything and temps are below 60C it still spins on 60% for another half of minute. Oh God...

 

[Intenditore]

I kingda tamed the GPU temps despite the performance is the cost. It can easily go to 80º without much noise, 10-20%. That's totally reasonable.
But as soon as AMD R9 370X is invoked it cracks my head with a ridiculous noise while the highest temps are below 70℃

I found a bunch of threads where people discuss the same s***y behaviour, but there's absolutely no solution or an answer what is this:

https://www.reddit.com/r/mac/comments/7rz0vg

https://www.reddit.com/r/osx/comments/74culh

https://discussions.apple.com/thread/4735947

https://discussions.apple.com/thread/8017453

https://www.notebookcheck.net/15-Retina-MacBook-owners-experiencing-fan-noise-problems.89544.0.html

Also, some info (with no solution) regarding inadequate throttling https://forums.crystalidea.com/viewtopic.php?t=1472

I'll be ok even with TGPro crooked nail and 99℃ temps, but how to avoid this insane throttling?

 

[Jaaaabs]

The thing that causes the fans to spin up is the GPU not CPU. If your GPU is idle (and in your screenshots you can see that it's not because the temps sit in the 50s) fans will stay silent - which is not necessarily a great thing I force my fans to start spooling up 10C earlier than what Apple defined.
There's no way to achieve what you want to achieve I'm afraid without some compromise, because physics.