I agree with you. It may be a problem with the audio file. Did you try with another one ?With that file, did you try the static-group command under the gigabit interfaces ? Even if there are some issues with multicast routing, with this command, you ...

Hi.what happen if you try to force the IP multicast traffic with the "ip igmp static-group 239.1.1.1" command under both g0/0 and g0/1 interfaces ?Are the data multicasted (sh ip mroute command) ?Hope this help...