Drupal Site Outputting Garbage

Recently we had a situation with a production website setup in a mult-site Drupal installation, where the site started outputting garbage randomly.  The site had been undergoing some maintenance, which included the installation of the signup module to enable users to register for events, as well as an upgrade to CiviCRM 2.0.

 Some users could see the site no problem, others were only able to load an initial page before running into problems, but most people couldn't see the site at all.  The garbage output consists of a blank page with random characters, many of which appear to be unprintable and so show up as squares, like so:

It turns out that this was a result of having Page Caching enabled.  Since this was a production site we had turned on Normal Caching as is recommended.  However, whatever configuration of modules or server settings we had on the server created this issue.  We were able to resolve it by turning off caching completely.  As this is a low-volume site this was not a problem, but we are still investigating the issue.  Telnetting to port 80 and issuing a GET returns PHP errors in bootstrap.inc indicating that output had already occurred.  Unfortunately I don't have the exact error or I would post it, and for obvious reasons we are hesitant to create this situation in a production site and so have to try to reproduce it on one of our development servers.  I would be interested in hearing any ideas or theories though.