Slow name resolution

I am administering an NT 4.0 domain with 50 NT 4.0 clients 1 pdc sp6a running DHCP and WINS, 1 member server NT4 sp6a running SQL 7.0. I’m having an intermittent issue with name resolution of the SQL server. From the client machines I can ping theIP address of the SQL server and get an instant response, but if I ping the computer name either it gets name resolution immediately, or there is a 15 second delay after you press enter before there is a response. After a minute or two it will go back to immediate name resolution. I have tried recreating the wins database, but the problem continues. Any ideas would be helpful. Thanks