[on-asterisk] White noise and choking on SIP lines

[Bruce N]

Hi Guys,
What causes white noise and intermittent cut off and choking on the SIP lines? 
Network is solid and it's separate from data network. All phones are Aastra and 
they worked fine for 1 year. I haven't got the chance to check cables but I 
doubt they can be the problem as it's a sip network.
Any experience?
Thanks,Bruce                                      
_________________________________________________________________