How to determine which program is making a certain sound in windows 7?

Those sounds come from your Google Chrome/Firefox extension called "Magic Actions for YouTube™. When any YouTube video is completely loaded these sounds are played. You can disable this feature in extension's options.

Your Windows 7 Volume Mixer shows sound level for each application.

Click speaker icon in tray, then click Mixer underneath your sound device to show applications that use that device.

Look at the sample screen. The green bar points Foobar as the source of sound:

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Edit 1:

If you cannot find your app here, it may mean the process is outside the scope of your current user priviledges. You may try following:

• Temporarily disable User Account Control or login as BUILT-IN\Administrator
• Alternatively, you may try to login as SYSTEM user, though I never attempted such a feat on a full desktop scale. Launch mixer as SYSTEM user use psExec tool: psExec -i -s sndvol.exe

Edit 2:

Google suggests: "HyperSound"