Repeated slow query notices(for a query that shouldn't be)

For a while now, I've received service messages that a query against a WordPress database was killed for running over a minute. It happens for two separate installs. This was originally just an occasional occurrence, but has recently increased to every few days, and I was curious if anyone else has seen this, maybe figured out exactly what the cause is, or could provide some ideas for hunting it down. The only plugins I've found for scanning queries involve things that happen while moving around in the application. But these errors always happen when I'm not in there, so appear to be from some scheduled process. (Posting of items is handled via queue, and the notices do not correlate either with me creating items or with publishing.) I haven't found a plugin or whatever that'll log that sort of thing.

The query in question is:

    SELECT ID, post_author, post_date, post_date_gmt, post_status, 
post_name, post_modified, post_modified_gmt, post_parent, post_type
FROM nwc_posts WHERE ( (post_status = 'publish' AND (post_type = 'post' OR post_type = '')) 
OR (post_status = 'publish' AND post_type = 'page') ) 
AND post_password='' ORDER BY post_modified DESC

The thing about it is that as far as I can tell, it's completely stock(ie. not obviously from a plugin).
All it does is return all published entries and pages. And, if you run it via phpMyAdmin, it's plenty fast. On an install that returns 1766 rows at the moment, it runs in well under 1sec, much less a minute plus.
Any ideas?