Determine whether you’ve configured any invalid forwarders. That would cause the DNS server to try to use the invalid forwarded server for name queries’ zones where the DNS server isn’t authoritative. If the forwarder doesn’t exist, the DNS server will have to time out the resolution request before it attempts to resolve the name itself.
To find and delete invalid forwarders, right click your DNS server in the Microsoft Management Console (MMC) DNS Management snap-in and select Properties. Select the Forwarders tab. If there are any invalid forwarders, click the Edit button. Select the invalid entry, and click Delete. Click OK to all dialog boxes to close them.