PS4 CUH-1115A unbearably loud fan

Hi @ all,
The PS4 was purchased in late 2014, everything was running fine and the console was actively used up to 2018. Apart from the slow WiFi download speeds which were fixed at some point I have not experienced any other issues with it. To make the long story short… the console was barely used in the next years although left in rest mode for the most of the time just sitting there.
To my surprise there was not that much dust inside when disassembled, anyway I applied some Arctic Silver thermal paste and went on. It turned out not only to be completely in vain but the FAN now sounded like a a jet engine without hush kits… like those from the 50s. Recently had some time and decided to give another try. Here is what I have done:

-Installed 1TB Samsung SSD and an 1TB WD HDD as extended storage.
-Applied new thermal paste (MX4) and new thermal pads (Thermal Grizzly)
-Cleaned everything of dust once again
-Made sure that the EMI shield are bended properly and there is no gap between them and the CPU/RAM
-Reinstalled system software 9.00

Unfortunately the fan issue was not resolved… maybe even got worse. Here are some more observations…

  • The fan starts as soon as anything is run… does not matter if it is spotify or RDR2. Not heard on the home screen or menus though.
  • Fan speed control seems to be working… 3 different speed modes can be heard. Even the slowest is ridiculously noisy, full speed achieved in less than 5 minutes in any game.
    -Once at this ‘take off’ mode it will never go back to slower speed… unless I quit and close the application.
  • I have never experienced any overheat shutdowns or BLODs.
  • The clamp on the APU is installed correctly and tightened properly.
  • However, if I try to tighten it further (less than 1/4 turn) the fan goes into another superspeed mode… even louder than the loudest while running games. As soon as I start to loose this 1/4 turn… it goes back to whatever mode it was in before.
    Generally speaking the noise during normal gameplay is comparable to an indoor A/C unit.
    I suppose there is something wrong with the temp sensor(s) readings but could not find anything on this.
    Is there anything else I can try?

Does the system feel like its putting out hot air, or is it cool? Also, if you get the chance could you check the thermal paste and send a photo of it?