Protected rtmp playback issue

I am running FMS 4.5.7 (r6008) on a Redhat EL5 machine.  When I enable PRTMP and try to stream mp3 or flv files, the first 2-3 seconds of the file plays silence and then the audio fades in mid-sentence.  I can consistently toggle this behaviour by enabling/disabling PRTMP in my Application.xml file (with PRTMP off, the file plays fine).  The logs look like the file streamed without any issues.  I have tried with JW Player and JPlayer with identical results.  Has anyone else experienced this unwanted silence at the beginning of files streamed using PRTMP?