MP4, WMP12, MovieMaker & Windows 7: No sound Options

[JRV]

My Windows Mobile 6.1 phone (HTC Touch Pro) saves videos in MP4 format. When played back on the phone, they have video and sound. However, when I move the files to my Windows 7 (RTM) PC, WMP & Windows Live MovieMaker play the video portion, but there is no sound.

On the advice of a poster on the microsoft.public.windowsmedia.player Usenet group, I downloaded and installed FFDShow, using default settings, which appear to include enabling MP4 decoding, and I still have no sound from the MP4s. I'm a multimedia newbie; any idea which of the 10-billion FFDShow options I need to set?

TIA