Invalid page header

Along similar lines to other recent posts I've noticed in the logs some
"Invalid page header in block ### of relation ...". errors. Given that
we have two basically identical s/w setups (ubuntu 6.06 LTS, PG8.1.4)
running on different h/w and only 1 box is reporting these errors and
based on the feedback to other similar posts, it looks like a h/w issue.
I'd like to hear the lists collective wisdom on what would be the best
way to identify what is causing these errors, given that there are no
system-level errors being reported.

Robert