In most games, DPCM channel is used only a part of the time :
For example, in Fire Emblem, only a quarter of songs uses this channel. In Earthbound (that looks like have the same sound programm), DPCM channel is there when you're walking, but it's silenced if you open the menu (that's really crasy).
In other taclical games, like Famicom Wars and Just Breed, only 25% of songs uses this channel. In FW, it's usually not used during the war, but it's there only for intro, etc... In JB, it's usually unused in villages and it's used only in the battles (out of villages), exept at the begining.
For a last example, Final Fantasy3j uses just $4011 to do ticks impulsions to simulate kick drum (or something like this). This is used only for battles, and the noise channel is also used only in battles (exept sound effects).

That's strange, isn't it ?

Bregalad, Ent from the woods of Fangorn