Regular short burst of network activity approx. every 4-5 seconds?

Not a big issue, but I would like to know what the short burst - 0.4Kb/s (up and download) every 4-5 seconds is all about?  I use 'Netmeter' to monitor network activity.

 

I know it's related to NIS 2009, as it stops if I stop the NIS service.

 

I don't have 'Pulse Updates' enabled, and I believe if I had, they would occur at intervals counted in minutes, not seconds.

 

Any ideas anyone?

 

Thanks