Well its a pulse engine... that's no big secret. The big concept was a SCRAM jet / Pulse engine abomination that would work and be extremely fast at 100,000ft. The SR71 did 85,000ft with RAM jets, and to this day stands as the record for fixed wing flight I believe. I dont think anyone really knows what it would sound like... but Ive never heard any form of pulse engine sound like anything else other than a bunch of little booms.
Heres an example of how a Pulse works... a fun kitchen made one. Concept is similar, and dopplar effect would make things sound different if it were in a plane.
http://www.metacafe.com/watch/1036326/how_to_make_a_jam_jar_pulse_jet_that_works/