Can you check "Hardware version:" string under "Sound Blaster or compatible" Properties in Device Manager on both 486 and P3?
I can't seem to find that particular detail on either computer.
In further testing, the P3 isn't as bad as I thought. If I play the sound clip in media player, it is quite badly distorted, while if I play the same clip in sound recorder, it is mostly OK. So it looks like windows media player, assuming that you would have a 16bit sound card, was munting the sound output, probably due to rounding errors.
I still get a lot of clicking on the P3 when playing though sound recorder though, I wonder if your newer firmware has already fixed that.