Doing voice-overs? The ‘voice talent for hire’ site Voice123 says Shun the Line In socket on your PC’s sound-card. By using it…
“you’re giving your sound card a noisy, unbalanced input”
What you need, apparently, is a “external digital interface” with a USB connection. The article doesn’t specify a solution — but is illustrated by a picture of an M-Audio external socket box, so presumably that’s the intended solution.
[ Hat-tip: Dulci ]