High speed UAP sound in 2.5 seconds.

Bright sunshine, occasional cumulus clouds.  Sitting under covered porch reading.  Heard a startling abrupt sound of a low altitude missile-like object directly overhead and it quickly sped south.  In the three porch  steps it took to get a clear view it was gone. 2.5 seconds duration.  No vapor trail. I have seen many high-speed low altitude flyovers of military jets, and I learned that the sound is not detected until the plane is overhead.  This sound matches that characteristic except for a major difference.  This object had a thin faint sound. The sound was like air rushing over a cylinder or fuselage.  There were no engine sounds, no thundering afterburners, no loud rushing sound of a military jet.  No doppler change.  It was gone in about 2.5 seconds.  
Never heard such a unique aerial sound as that before.  My perception is its speed was hypersonic minus sonic booms.  I have no air tank systems, no liquified gas tanks (venting).