NGOHQ is reporting that Creative Labs is blaming NVIDIA for cracking and other sound quality issues when an X-Fi sound card is installed in an nForce 4 motherboard. This reminds me of the good ol' days of installing the PCI Latency patch on VIA chipset-based motherboards when using a Creative Labs sound card.
"We have observed through direct observation of the PCI bus on the nVidia nForce 4 motherboards that when the crackle symptoms are occuring, the Soundblaster X-Fi card PCI bus master memory requests for audio data are being held off (not serviced) for very long intervals. We have observed peak holdoffs of up to 2 milliseconds in some cases. This is unusual chipset behavior that is beyond the ability of a hardware audio accelerator to compensate for in its internal buffering. The SoundBlaster X-Fi tolerance for these PCI holdoffs is approximately 120 microseconds peak holdoff, with a 1 microsecond average holdoff."