The maud file extension is associated with the Amiga MAUD audio format, developed by Electronic Arts and Commodore in 1985. The MAUD is used for an 8 or 16 bit Amiga sound format. Most likely obsolete.
WavPack lossless audio compression. Note that, when converting .wav to this format and back again, the RIFF header is not necessarily preserved losslessly (though the audio is).