Precision 7560, fans running at full speed without any applications started

Hello everyone,
Since yesterday the laptop fans suddenly started running at full speed without any application started. I cleaned the fans, renewed the thermal paste and updated the BIOS to version 1.27 without obtaining the slightest improvement. No thermal management adjustment in the Dell Optimizer makes any change. Windows 11 23h2 operating system with all updated drivers. When I unplug the power supply, i.e. the laptop runs on battery power, the problem disappears. Any idea please ???