I want to share the modification that I decided after studying the wiring diagrams and searching in vain on the Internet with max. care to solve yourself. So it's easy after all.
1. Open the top cover of the TRX
2. There is a fan connector under the speaker and a resistor opposite SMD R204, 18ohmov.
3. Carefully remove it with a micro soldering iron and replace it with a value of approx. 82 ohms.
This change will reduce the speed in the first stage of ventilation. There is no disturbing blowing and the second stage works unchanged (at a higher temperature).
I still want advice on desoldering R during modification. It is possible to use a preparation made of copper tape formed around the tip of the microsolder and with recesses for the size of the soldering points R-(SMD resistance), thus heating both points of the SMD resistance at the same time and not overheating the circuit board. It's at least a little better quality work. In the extreme case, the available miniature resistance from the drawer supplies, installed in a standing position, can fit into the cleaned place. I used SMD 100 ohms 0.125W - it is more professional and visually. A micro soldering iron is a necessary equipment. For information, I also state that the control of the first TRX ventilation stage is controlled by Q205 via R204 and the second stage by Q204 via R202-2.2ohm.
Conclusion: After the adjustment, I do not notice excessive noise from the air flow, even if the blowing takes a little longer, but I do not perceive it as disturbing at all, especially at night when the volume of the TRX is turned down. You can also check it in the service manual.
Thank you for your attention and I remind you that tampering with any device is at your own risk. OM5AMJ Miro.