If they keep logs like my school does, they should be able to tell you exactly what IPs are contacting you (or you contacting IPs), or things like that. Try asking them if they have any more information as to what might be causing the problem. If anything, have network operations look at your computer themselves, they may be able to determine more concisely what is happening.
Make sure there are no bridged connections (i.e. if you have a laptop, if you are broadcasting wireless, or if you have two ports connected to the computer) ... it is detectable if you have Windows. Netops here doesn't like that because it is an unauthorized access into the school network.
