Speaker Crackle

Not being there, a couple things to check are interference sources in the nearby area. Wireless mice and keyboards are known culprits. Nearby lines, things like that.

If the blowing helped the card, it could be a physical problem such a slight gap in a connection, or a bridge of material across a connection. Could also just have allowed the computer to cool or change state while you messed with it. You might experiment using a high pressure air can on it while the computer is in operation to see if it changes things, rather than turning it off.

Does the sound vary in frequency or occurence with CPU load? Possibly a change in usage patterns? Some cards have stress issues and without proper overhead crackle horribly, which updated drivers can sometimes fix. There are also some known issues with heavy USB load being transfered over to the sound card.

A mute on Line-In may also help, as it could be transmitting false signals from the connection.

Also, what's the card type, as there are a number of card lines (particularly the Audigy line) which have vast crackling problems with no tractable solutions.

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