Ok, i did get double channels, but i dont really care about that. What hacks me off is Metroid glitches after update. Pointer (cursor) is out of alignment, scanning thing leaves menu graphics flashing constantly, wonky forward action (cant poperly open locks)... Before update, on 2.2e, everything was fine. 3.0e stuffed the game good.
I heard this problem in a few other forums, pretty much everytime its been asnwered with, "MP3 will only work correctly if you change your wii settings from 50Hz to 60Hz mode."
For now I think there is no solution to getting rid of double channels.
It's too late for you now but this might help others, and I know it sounds dodgy but many have confirmed this to work.
What you should have done is while your game was updating, after about 15% of the way, you should have shut off or pulled the plug on your wii, the game is supposed to work after that with a brickblocked backup of the game. No double channels.