TF2 - little hiccups and gaps on net_graph

[pilger]

Hey guys.

I'm renting a server on a host with the following specs:
Dual Intel Xeon QuadCore 2.4Ghz
8Gb RAM
2x 300Gb SAS15k
Link 30MBps FullDuplex
SO: Windows 2008 Server
Game: Team Fortress 2
Start-up command: n / a
Mods: sourcemod (but the problem presented even without metamod and sourcemod)

I'm having these weird gaps on my network graph without showing any loss. During the gaps, everybody experience a little hiccup, which is very disturbing to gameplay.

It's clear on these videos i've recorded:
http://www.youtube.com/watch?v=ArWe_ODu2-Y
http://www.youtube.com/watch?v=GgWldsyWNIQ
http://www.youtube.com/watch?v=Y9TPsEbBT08

Is this normal? What could be causing this?

Thanks in advance!