Have the same problem. Had a DR400 a long time ago, replaced it with a brand new DR600. Image is ok, but audio quality is really really poor. Vids from my 400 have workable audio, 600 is just noise...
Hope this is fixed soon!
Is there any way for a temporary fix? Has anyone experimented with using 720 recording, 1/2/3 minute recordings or 16/32/64gb cards to see if changing these things makes a difference?