My computer keeps making a knocking sound randomly. Is this a virus or Zonealarm or another program trying to notify me of something?

Impending hardware failure maybe. Is it coming though the speakers or from the tower, (or box)?

Maybe? Trojan.Visages http://securityresponse.symantec.com/avcenter/venc/data/trojan.visages.html Trojan.Visages is a Trojan Horse that does not copy itself, drop files, or have a malicious payload. When this Trojan is run, it causes continuous activity on the A: drive. When Trojan.Visages is run, it performs the following actions: 1. Displays the message, "Welcome to W32.2faced," when first run. 2. Makes continuous calls to the A: drive, so the drive is always spinning. 3. Adds the value: "Microsoft Corporation"="" to the registry key: HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion\Run 3. Loads at startup as a System Tray icon that looks like the Norton AntiVirus Auto-Protect icon. If the icon is double-clicked, it will display the message, "Are you Ready for when Jesus comes?" Clicking OK displays the message, "I Am." Free virus scan http://housecall.trendmicro.com/

It could also be ICQ or YAhoo messenger telling you that someone in your friends/contact list has just come on line, obviously this doesnt apply if you don`t use those programmes!!!! Woof