Hi Adam,
Unfortunately the quickest way to find the offending plugin is to start disabling your plugins (other than TubePress) until the problem goes away. I would start with disabling 50% of your plugins at once. If the problem goes away, you've narrowed the candidates by 50%.
You might also want to try switching to WordPress's default "twentyeleven" theme to rule out any interference from your theme.
You could always put your site into maintenance mode so your visitors don't get a weird experience.
Hope that helps...