Period of silence

Anyone else experiencing this or have done the past few weeks? Basically on a call and there is a 5 second silence.

Help?

Using a Sip phone?
Through a regular phone?
Only when calling out?
Only when calling another extension?
Always?

The more details you provide the more likely someone is to help. Also the more details you provide will increase the quality of the response.

Using a SIP Phone and calling outbound not an extension, ports all closed apart from 50/60, has been fine for the last couple of years and in the past 3-4 weeks it has happened frequently, thought it was some dos attack but cant seem to find any ryhme or reason.