Voice quality good, ringing quality bad on IAX2

Hi all,

I have a strange problem such that when I make outbound calls (on a Gradwell IAX2 trunk) the ringing signal is of terrible quality. Once the end user has answered the audio is good and we can hear each other loud and clear.

I know it’s not the handset as this problem does not appear when I’m using SIP via Sipgate. It’s also not that I’ve selected the wrong country or tone setup as (roughly) one in 5 of the ringing “sounds” are perfect.

I’m using Asterisk 1.6 with SNOM 370 handsets.

Thanks for any input.