i recorded several voice memos from my 3gs and one particular recording did not have sound during the playback. the rest were perfectly fine. all the recordings i had were over an hour and the file size of the 'soundless' recording is consistent with the rest (40-60mb). the file is a .m4a and is playable in vlc, itunes, quicktime, iphone but just that no sound came out. i'm quite sure i did not block the mic while recording as i have always placed it on the table while recording. any help/advice/ideas/remedies to the problem?