Helping people with computers... one answer at a time.
If you have speech recognition always enabled it can cause your computer to "go nuts" because of the different sounds it interprets as actual words.
My computer behaves erroneously frequently. It suddenly closes all IE browser windows, opens start menu and repeats this process. OS: Windows XP. In the task manager I saw "sapisvr.exe" during this process sometimes, not all the time.
It's a really weird thing to watch - it's almost like your computer has suddenly become possessed. But the question holds a clue: sapisvr.exe.
Chances are, though, the computer is really only doing what you're telling it.
Sapisvr.exe is Microsoft's Speech Recognition engine. When enabled, it listens to what's coming in on the microphone and attempts to interpret what it hears as words, then enters keystrokes to "type in" those words it heard.
That's nice, in principle, but if it's always enabled it can cause exactly the odd behavior you describe. You make a noise (just about any noise can cause it to think it's heard a word), and keystrokes get entered. Or ambient noise is enough to cause it to try to recognize speech.
Normally this feature should be disabled, but apparently some PC manufacturers or others enable it by default.
Go to Control Panel
Click on Regional and Language Options
Click on the Languages tab
Click on the Details button
Click on Speech Recognition
Click the Remove button
And if you're wondering why this could be happening if you don't have a microphone, look again. Many laptops in particular have built-in microphones, and I'm lead to believe that some other computers may as well.