Are you on a shared or a dedicated server?
if you have a large forum which gets lots of spiders, but hardly any new posts (once a week or less), then the triggered micro maintenance which is done after each post, can become rather large.
updating the "post view" counters for all posts, is done after each new post is made. if the lapse between new posts is a long period of time, and there are several new post views, the micro trigger could be your answer, in addition to if youre on a shared server where your host has limited the amount of resources to your account, or another website is hogging them.
