Major distortion on voice recording

Voice recordings from Confbridge or the Dialplan on our newly-configured system are distorted and full of noise. The waveform shows clipping and added noise. We are using Asterisk 11 on Ubuntu 12.04. Strangely, this machine was running Asterisk 11 on Centos before we reconfigured it, with the same conf files, and voice recording was fine. This is a physical machine, and we are using VoIP-only from a DID supplier using SIP.

Be grateful for help.