Duplicate ringback tones on IAX trunk

I’ve recently migrated from Trixbox to the FreePBX distro. Trixbox just had too many ‘broken windows’. So far I’m loving the more up-to-date-and-everything-working-as-it-should experience of the FreePBX distro.

I did my migration on a ‘no change’ basis so as far as possible, I copied over my config from the Trixbox ‘as-is’. Obviously there are some differences and additions in FreePBX distro.

One of the problems I’m having is with the ringback tone on outgoing calls. When the call is first dialled, I get a single long ringback tone which I think is the standard American tone (I’m in UK). Then, after a couple of seconds (as the trunk connects) the tone changes to the UK cadence. If the call is routed over a DAHDi trunk, then the UK tone replaces the American tone and I think it is coming from the PSTN. If the call goes out over one of my IAX trunks, I get both tones superimposed. This did not happen with Trixbox.

I’m sure there is a configuration I’ve missed somewhere, I wonder if anyone can make any suggestions as to what might call this?

If it helps, we’re using Cisco 7960 IP Phones with SIP firmware POS-3-8-12-00.