I’ve got Aastra 6730i phones working OK. I can dial between extensions without problems but when receiving an external call I hears noise. I put an IVR and the IVR is ok but as soon as the call is transferred to the aastra extension the noise starts, like a wrong codec being used. I tried changing codecs on the phones an on the pbx, forcing g711, etc. with the same results.
If you suspect the codec, take a look at the logs and see what kind of transcoding is happening. While it won’t just solve the problem, it might give you a better idea of what the problem is. If your incoming call is g711 and your phone is g711, you shouldn’t have to do any transcoding, but if you are switching to alaw or ulaw somewhere in there, it could easily cause all kinds of hinky problems (g711 to ulaw to g711, for example) and could explain the problem you are seeing.
If your incoming connection is actually ulaw and you then transcode it to g711, then transcode it again to ulaw (for something in the server) and back to g711 (for the phone), you could easily be messing yourself up.
That’s just a guess, though.
having the same problem, think is related to echo cancellation errors. Might have to do with codec too. have you found a solution? here’s the thread relating to my problem >>> Distorted echo inside the network on FXO channels