This problem is not limited to any computer make nor 64-bit Windows 7, I get the exact same behavior on a custom built machine running Windows 7 32-bit.
Next time it happens do me a favor, go up to the taskbar and open the "Realtek HD Audio Manager".
Mine literally blinks on and off changing screens while at the bottom it repeats... "loading audio devices"
I can't tell for sure but it looks like the Realtek driver
is losing either the mic or line Input device and resetting. It's the reset that's causing popping, crackling and skipping.
I just downloaded the (turn_off pullmode) drivers
posted earlier, they seem to be working but who knows, I'm liable to play a youtube video and it will start up again.
If it starts again I'm going to try a couple ideas.. if I have any success will post back.