NO audio for 2-5 secs every 4-5 minutes

Hello,
We’re having hard time with an issue with Freepbx13

NO audio for 2-5 secs every 4-5 minutes, the voice is crystal clear and suddenly everything stopped and nobody hear each other.

I turned the SIP Debug and and RTP debug on, and when this append in the cli everything stopped for the same time we do not have audio.
The server specs is:
Intel Xeon W3520 4 c/ 8 t 2.66 GHz+ 16 GB 2 x 300 GB SSD

Please help!
Need advice…

Pierre

Check your messages

/var/log/messages

also run the command top while making a call and post here the output.