asterisk users - Jun 2006 - Voicemail beep doesn't end

I've hit a problem with Voicemail.

My call gets answered but the 'beep' before I should start recording a
message doesn't end - it gets a little quieter.

I can leave a message over the top of it, but the recorded message is
very quiet.

Any idea what might be the cause of this problem?

My config is pretty basic at the moment:

[general]
format=wav
attach=yes

[default]
101 => xxxx,Russell Horn,russell@localhost

Everything else seems to work fine with inbound and outbound calling
using SIP and IAX2 trunks.

Thanks for any suggestions,

Russell