At least one of the two HDDs in my T41/WinXP/SP3 audibly goes into standby after a few minutes of inactivity. This happens even when the system is connected to a power outlet, and with power savings setting "Desktop" (= no standby at all for HDDs).

Any idea what may be the cause?

I would try booting the system from a bootable CD to see if drive shuts down when the OS isn't loaded. That would give you an indication if the problem is hardware or OS related.

Thanks for the suggestion!