Hi pols,
Do you have a third parties sound card?
Or just the built-in motherboard sound?
If you have a third parties sound card.
It is possible that there is a link with the heat if the temperature is high, of course.
For example, if the graphics card blows hot air on the motherboard. And if the sound chip are hot....
Or even directly on the third parties sound card.
The result of this hot conditions, heat environment, on the electronic components, will you may hear sounds, strange noises when you use the microphone or headphones.
Of course, if in the place where the computer is, it's hot, very hot, it does not really help either.
If the chip is too hot, it would be best to put a heat sink on it.
I hope this info will help you.