It seems to me that our server freezes every 30 days around noon due to the huge utilization of xvda data transfer partition - writes are 50 times higher than normally (according to the health monitor in plesk). This seems to me as the reason why the apache & co becomes instable as (for example) all apache's processes are waiting to write their log (according to the service's full status).

I am, however, unable to find any scheduled task that would be executed during that period. I have checked both cron and anacron setup and there is only one monthly anacron task which is not executed (according to the /var/log/cron - and there is nothing unusual) around noon.

Are there any other places where to look for periodical processes?

(I am just about to ask server's provider the same question about any external maintenance run around this time but I don't expect them to run anything time/resource consuming during the day.)