Uptime outages

I am getting short but regular downtime on most of my sub domains., but not main domain. Each subdomain is getting about 3-7 outages over a 24hr period. They are not going down together, so the server must be ok (right?).

I have contacted server support, but they don't understand the issue - they say my sites are pinging ok. Should I be able to see outages in error logs or something?