PCI Bus Error

Hi, once a month or every two weeks approx. my ML 370 G5 server running ESXi 5.5 Update1 crashes and the Integrated Management Log reports "PCI Bus Error (Slot 1, Bus 0, Device 30, Function 0)".

How can I tell which component this is?

I'm running an offline diagnostics, but from google results so far that doesn't usually return any answers.

http://h30499.www3.hp.com/t5/ProLiant-Servers-ML-DL-SL/PCI-Bus-Error/td-p/4285769

http://h30499.www3.hp.com/t5/ProLiant-Servers-ML-DL-SL/ML370-G5-ASR-Boot-with-PCI-Bus-Error/td-p/4315885

Believe firmware and software is up to date as can be.