Lag spikes on server when using voice chat

Whenever someone uses voicechat, my server just get a huge lag spike.Any idea?

CPU In_(KB/s) Out_(KB/s) Uptime Map_changes FPS Players Connects
33.17 4.06 5.13 6 0 66.47 2 2

Processor : Intel® Xeon® CPU X5672 @ 3.20GHz
CPU Cores : 4
Frequency : 3200.185 MHz
Memory : 4096 MB
Swap : 512 MB
Uptime : 1:12,