+1 on blaming Realtek NICs.
I built a machine in the past two years that had Realtek NICs (horrible oversight on my part). Put pfSense on the box and it locked up randomly requiring a reboot to resolve the issue. No log entries or anything else. I also put VMware ESXi onto the same box and had it purple screen a few times (even with injecting an in-line patch to support the NICs).
IMHO, newer Realtek NICs can hang your box w/o logging issues in the OS. Avoid at ALL costs.