IUSR accounts being used to login to remote server

[mgreen]

I have a Plesk Panels v8.6.0.5 server. I have several domains with databases on the same server. There is no issue that I'm aware of with the sites on those domains accessing their databases. The connection strings being used on these sites all are using user account created directly in MS SQL server. However the IUSR account for each one of the domains is trying to log on the database server remotely once a second constantly. There is not a scheduled task, script or anything else I can find that is the cause of this on the There is nothing in each site displaying this behavior that is "calling" the server directly. There are only a couple of sites that are displaying this behavior.