Actually, I've run across this before too. I'd be sitting there late at
night in my room coding , and out of my speakers would come voices! Believe
me, it freaked me out too. The voices would come at random times of the day,
and it wouldn't matter what application or OS I was running. It was entirely
random, I thought. What's worse is that I thought I was the only delusional
person around, until one of my friends mentioned the exact same thing to me
one day, and I nearly jumped out of my chair. :-)

I couldn't track it down for the longest time, until one night the night
watchman for my apartment was walking down the hall outside my room (my door
was open), and then I heard his walkie-talkie (or long-range radio of some
sort) beep. He then spoke into the walkie talkie/radio, and lo and behold,
my speakers came to life and rendered a _very_ scratchy rendition of his
voice - bad enough sound quality that I couldn't make out exactly what he
was saying, but it was recognizable as being his voice, if you heard both
him actually talking and the speakers at the same time. =)

I immediately flagged down the night watchman, and together we found out
that if for some reason his walkie-talkie/radio was set to a particular
channel, the speakers and/or sound card in my computer somehow picked it up
and played it. I have a Sound Blaster Live, BTW, along with the Cambridge
Soundworks 4-point speakers. My friend has a laptop with a different sound
chip, but has roughly the same speakers (older model). I still don't know
exactly what causes it, but..

In any case, nowadays I turn off my speakers before going to sleep, so I
don't get woken up in the middle of the night. =)

later,
Edwin