I timed it (on Firefox 1), exactly 30 seconds. I've only noticed it on Arnies. Says on mine, "transferring data from akmeter.akmos.ru"? But since the page is cached, it doesn't seem to actually affect the page, only the tab icon and the status bar.
Aha, solved it!
It's updating the currency converter! Look at akmos.ru, it has an exchange rate thing called Forex, which is the name of the thing on the bottom left of the page here. It blinks every thirty seconds to update the exchange rate.