ok I have a work around. You have to go into the mixer and give every sound channel you want to hear the sound font "MS Basic", which is the only sound font installed by default. You have to download a sound font pack, then assign the metronome, say, "Celesta" or something like that, and then it'll shut up. Wow.
With that out of the way, there don't seem to be any other nasty surprises at least :|