Metal popping, or Chips frying??
It has to have a source from somewhere (yea, I know, that's obvious).
If the mic input is enabled and there is no mic connected, the inputs could be floating causing the noise, or it could be something else.
Check the mic is not enabled:
Double-click sound icon in system tray,
Is the mic volume slider visible? If it is...
Click "Options" then "Properties"
It will show 'Adjust volume for' and 'Playback' will be selected.
Scroll down the list and find "Mic Volume" and uncheck it.
Click your way out by clicking OK to everything.
Noise gone? Yes=best answer No=continue...
Go back to the mixer again (dbl-click speaker icon)
Click Options again, Properties again,
This time click the drop-down box at the top (Mixer Device) and see if there is an input device present, if so, select it.
This new box will show 'Adjust volume for' and 'Recording' will be selected.
See if anything is checked that you are not actively using. Here's the catch, Something must be checked or the "Ok" will disappear, so have one item checked that is not suspected of being your source of noise, like 'Recording Control' because it can be muted in the volume control box that will appear as soon as you click Ok.
While you are there... If you saw a digital input possibility in the list of input devices and you are not using an outside digital input device, you can un-check any devices that show there (SPDIF).
If you unchecked 'mic' or 'line in' or anything else but left one un-suspected item checked and clicked Ok, is the noise gone?
If yes then life is good, if no, then something is getting into your audio buffer or your sound chip is about to loose it's smoke (everything electronic runs on internal smoke, if you let the smoke out, the device will quit working).
Last but not least, update/re-install the sound driver.