Noises associated with earthquakes are an interesting phenomena. We have several
old tape recordings here from the 1950's and 1960's. Usually, earthquake noises
occur in areas where rocks are old and very brittle. For example many events in
the northeast U.S. and Great Britain are associated with low frequency noises.
Noises are usually also associated with very shallow earthquakes. The Nisqually
event was about 50 km deep, too deep for noises to carry to the surface, so it would
be surprising if there were loud noises associated with this earthquake.
The noise is probably the sound of rocks scraping other rocks, although this has
never been proven (at least to my knowledge).