This is more than likely attributed to NetBIOS
This is due to the behavior of Windows servers that use NetBIOS (as well as DNS) to resolve IP addresses to names using the "gethostbyaddr()" function.
This shouldn't be too big of a concern for you.
You might want to disable the NetBios Over TCP/IP protocol on the interface and use the LMHOSTS file for the servers that needs to be resolved using NB names. That might be the case e.g. of the SQL Server.
You should no more have any NetBios Lookup Query trying to go through your firewall if you do so.
Some posts about the same issue: