Not sure how creditable they are,
but I recall reading about these
interesting titbits...

Lobsang Rampa mentions caves he
went into whose walls were like
smooth marble where the rock had
been 'melted', without heat, by
some sort of sound generating
device... perhaps ELF? Would make
those massive tunneling machines
redundant pretty quick.

In a book Supernature there's an
account of a giant pea whistle
about a meter in diameter, driven
by a compressor, that generated
about 7Hz. The operator who stood
beside it ended up with his bones
and organs basically dissolving,
just his skin kept him together.

Acoustics, especially what you
can't hear, is fascinating!