I had this same issue, if you're using MCpatcher to install mods, put forge below modloader in the list. If you have modloaderMP also, put it between them.
If you're not, install forge after modloader, that way forge's files overwrite modloader's.
You may have a different issue, but I hope this helps.
I'm having the same issue as him up there. forges sd.class overwrote audiomod's and still no joy, maybe some other underlying issue? I looked over all the info MCpatcher spews when MC runs and I don't see audiomod in the list, you think risugami might need to update something?