When dealing with GrimE games, the .WAV files are not normal WAV files, but compressed. In the LEC action games (such as Phantom Menace) and in some instances in Grim Fandango, they are uncompressed, however. The files contain the (compressed) RIFF block, along with, if compressed, compression info in an MCMP block.

(
blMCMP	block	MCMP block (only if compressed).
)
blRIFF	block	RIFF block.