🚀 go-pugleaf

I've been using Debian for over a year now, and my system seemed to be
working fine (except for some incredible hassles with an AWE64 soundcard
that is now residing in my old-hardware pile).  However, I've found a
really strange problem with my hard disk that I'm hoping someone can
help me with.

After much experimentation and several wasted CD-Rs I figured out that
I was getting buffer underruns - which was rather surprising considering
my hardware:

Sony CRX-100E 24x4x2 CD-RW
Clone PII/266 on a Gigabyte LX motherboard with 128 MB of RAM
WD 6.4 gigabyte IDE hard disk.
Kernel 2.2.13pre14

The system should have been more than fast enough to write at full speed.
However, experimentation showed that some of the audio files were being
read extremely slowly (< 100 kbyte/second).  Once these files were copied
(presumably to a seperate area of the disk) they were read at normal speed
and I was able to burn them onto a CD successfully.  

My first thought were that these files were horribly fragmented, but
that seems unlikely as there is still plenty of spare space on the disk.
fsck, when run on bootup, has not ever reported any problems either.

Can anyone suggest what the problem is likely to be?  Is it just a flaky
hard drive that I'd better start backing up ASAP?  Is it extreme fragmentation?
Is it possibly a kernel bug (unlikely, since I obtained the exact same 
results with 2.0.38, 2.2.12, 2.3.18, and 2.3.18ac10)?

Any help would be much appreciated.

Rob