No sound over Airtunes

When I play podcasts that are streaming from my iMac the sound and picture is perfect - but when I use airtunes from itunes no sound is coming from my Apple tv. I have tried with several different macs without luck

The Apple tv runs 3,0,2 with latest update from Atvflash - Itunes is latest version as well - we have tried with Mac with Leopard and Snow Leopard

Any advice?

Thanks

 Jus t wanted to let you know i had the same problem but i clicked on the bottom where you would select the express speakers and selected the multiple speakers option and increased the volume from there and that gave me audio immediately.