Speccy CPU fan speed almost always...very up high

[pierino]

I have an Acer TC-895-UA91 desktop running Windows 10 Home 64-bit.

Lately the CPU fan speeds up (almost continuously at about 680 rpm indicated by Speccy) and it's very noise. I wonder whether my CPU is overheating as Speccy shows CPU temperature between 43 and 55 Centigrade when the problem occurs. Motherboard voltages show as:

  Voltage
    CPU CORE    1.632 V
    MEMORY CONTROLLER    1.760 V
    +3.3V    2.976 V
    +5V    5.000 V
    +12V    11.904 V
    -12V    -11.968 V
    -5V    -9.408 V
    +5V HIGH THRESHOLD    4.032 V

and that -5V at -9.408 concerns me a little. Everything else works just fine!!  

Any suggestion

Pierino