Problem solved after some research and help from nvidia:
APIC timing (Advanced Programmable Interrupt Controller) on nforce2 chipsets is broken and causes hardware lockups under some conditions. This has someting to do with the C1 disconnect HLT command of the CPU. APIC is enabled over ACPI (Advanced Configuration and Power Interface), so I built a new 2.6.6 kernel without ACPI support and the driver runs properly. I have only Stereo Sound now (sound quality is excellent), but I had not time to enable 5.1 Surround. The lost Power Managenent features of APCI can be replaced by the older standard APM. Only insert apm module.
For some information about this problem see the extensive and sophisticated discussion
The noise (described above) is emitted by electrostriction of two transformator coils near the CPU. But the reasons for this are still not clear, although there are reports about it in the link above.
Thank you Nvidia for this excellent driver!