VoIP to cell phone "loud noise" issue

[treeves]

Several of my users are complaining about hearing a "loud noise (sounds like a modem picking up)" when an external person places a call to the campus and the VoIP system  using Single Number Reach (SNR) forwards to their cell phone.  The problem started about 3 months ago and it is getting worse.  All the user have company provided iphone 5s.  The 'loud noise" usually happens after 5 minutes and it seems to happen to the some users more than others.  I get dozens of calls each day but I have only had it happen to me once.  

We are running CUCM 10.5 (but was happening on CUCM 8.5 also). We use PRI for connectivity to the PSTN.  Is this a internal VoIP issue, a gateway DSP issue, PRI service provider issue or wireless cellphone issue?  Any body else seeing this same or like issue? 

[henry.ola_2]

Hello,

We are experiencing the same exact issue at the present time. We are running MGCP on the Gateways, CUCM 10.5, and PRI for connectivity to the PSTN . I would like to know if you have resolved this issue and if so can you provide steps taken to mitigate it.

Thanks

[Daniele Giordano]

Try to force a voice codec, e.g. G.711, disable comfort-noise, disable silence suppression, update DSP firmware.

Regards.