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

Speccy Speccy Bug Reporting
1

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


   <strong><em> -5V    -9.408 V</em></strong>


    +5V HIGH THRESHOLD    4.032 V

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

Any suggestion

Pierino