Here's another thought, since it's something I've observed in my bikes -- is there any wobble to the chainrings? Even with brand-new chainrings and cogs, you can get that awful rumble if something in the drivetrain is causing the chainrings to run out of true. I suspect it's because the chain alternately has to ride up each side of the chainring to stay meshed.
http://sheldonbrown.com/straighten-chw.html