The next time it happens, stay on the iHub page you're on, wave your mouse over the banner at the top of the screen, and look in the status bar to see the URL of the ad agency that delivered that banner. Popup code is usually embedded in banners.
Also let me know which banner you're seeing.
I assume this is only happening before you log in? Once you're logged in, assuming you're grandfathered or paid, all routines on the site skip right over any ad-delivery code.