What's causing crackling sound on my PC and how can I fix it?

i concur with your findings. here is some elaboration for you. PCI is a type of slot to which your sound card, if it is not integrated into your motherboard as i suspect it is, would be plugged (this is easily checked. if there is a card with sound related ports on it plugged into your motherboard and not integrated into it, then thats the sound card). latency on this slot would cause data to be sent to/from the sound card at an improper rate, potentially causing crackling. the latency tool should have corrected that. it honestly sounds like the problem is the speakers or the soundcard/motherboard itself. try new speakers or headphones and if it happens anyways, replace your soundcard. you can email me for more information on how to do this correctly.