I have recently noticed a strange phenomenon where occasionally I get video freezing then (in the resulting silence) I hear a HDD spin-up and the video continues.
It only happens very occasionally and I haven't been able to establish a pattern of events (other than being able to hear a HDD start to spin).
My initial assumption is that it may be buffering footage to RAM, spinning down the HDD and then not spinning it up again in time to prevent the freeze. Any other thoughts?
I will continue looking into it myself but at this stage I cannot even think of any keywords to google.

System (combined front and backend):
 - P4 3GHz
 - IBM Netvista Motherboard
 - 2GB RAM
 - Ultraview (DVICO) Lite DVB HDTV card x2
 - 40GB System HDD
 - 750GB Recording Storage HDD
 - 250GB Music/Video/Download Storage HDD
 - 256MB nVidia AGP (outputting to 1080p LCD via DVI-HDMI cable)