Thanks for the replies.

The problem is solved, not sure what it was (yet) as I've changed 3 things:
1) Swapped the V3800 Ultra Deluxe (which doesn't like Ali chipsets, maybe it doesn't like VIA chipsets either) for a GF2 MX.
2) Went from ME to W2K (After all those years installing ME became a ritual and I never had this problem before).
3) One of the IDE connector pins on my DVD-Rom was bent, maybe it corrupted the install.

I'll try to keep it short.
My Asus P3V4X makes strange popping/clicking noises when playing MP3's, also when I run F@H it doesn't finish a single WU (It keeps saying Early unit end).
But when I play a WAV file I don't hear strange noises.
I've replaced everything (RAM, PSU, Mouse, Keyboard, CPU, Sound card, IDE cable, HDD, Graphics card) except the MOBO (doh) and 2 NIC's.
I also did a fresh install.

First thing that came to mind was a power issue, but I don't want to buy caps if I'm not sure (the caps look fine).

The MOBO is 3+ years old...