I am in agreement with whichever PGC staffer said that the Wiimote speaker is ill-suited for the things they make it do. The little thing is overdriven and has crackled on me many times already.
HOWEVER..... There is a way to turn it off, and not only that, but make the sounds it otherwise plays go through the standard sound system! Click on the little "Home" button on the Wiimote, and you get an in-game system menu. Near the bottom are readouts for the four Wiimotes, which contain battery charge levels at the top. Put the cursor over it (enjoying the gyrosensor's ability to cause the cursor to rotate

) and click it. Amongst the new settings you see here is a volume control for the Wiimote speaker. Turn it all the way down... and all the sound is played through the standard speakers.