Power Supply

The popping is typically from the power supply kicking on and off to the sound card.

Do you experience hissing or whining noises when the CPU is changing loads? If so, you're either getting noise from the motherboard or the power supply.

Sometimes changing the sound card can make a difference but I think most of the time its due to poor build quality on motherboards / PSUs.

As far as how to fix it, I'm not sure there is anything simple. Could be the card or MB or PSU, in my experience.