Call Of Duty 4 (COD 4) runs well on the single player game option, however, there are problems when you switch to the multiplayer mode. First, ascertain your computer model and look for a sound card update. If video games are installed on a secondary partition, download the latest BIOS updates for your system's motherboard. Some soundcards need additional instructions and setting the sound tool is done by enabling Stereo Mix. In addition, a USB microphone plugged in the system's USB port may solve the issue. It is observed that while connecting a microphone jack to the sound card, a pair of headphones or RCA connectors will eliminate the problem. Plugging into a microphone jack can result in breakdown of components in your system.