Random, Transient 404s in wp-admin

What conditions will trigger WordPress to display a 404 page other than a given URL not existing?

I have over a dozen WordPress installs, and some of them are on DreamHost (which is starting to seem like a mistake). The ones on DreamHost—and only the ones on DreamHost—exhibit an occasional bug that I cannot understand. When using the various functions of wp-admin, such as browsing past posts, editing a comment, etc., I will periodically receive a WordPress 404 error. This is while viewing totally mundane URLs — /wp-admin/post-new.php, for instance. A reload of the page just about always resolves the problem, although sometimes a series of reloads are required to get the page to appear.

I’ve tried to determine what conditions will trigger WordPress to display a 404, but I’ve had no luck sussing out where to find that within the code.

My guess is that this is because of DreamHost’s chronically overloaded servers. Perhaps it’s killing off a MySQL query in progress, which causes WordPress to receive a false response as the query result, which simply displays a 404 for lack of any better response?

I’d love to hear either a) where to find WordPress’ 404 triggers or b) what’s causing this, should somebody know.