Re CVRs. Is it possible the heart beat is just that, e.g. somebodies chest in contact with the structure near the CVR?
I have been wondering if there is a case for higher tech CVRs. They are now being used for much more than the original voice recording task. If they were fitted with a wider spectrum recording device and had a geophone type of device fitted directly onto the structure they would then record a lot more info without additional wiring etc? This might be a method of getting more info out of older AC by only refitting the existing devices. Some accidents seem to be getting into more obscure causes, due to the elimination of the basic causes. By definition they are bound to involve more of the older AC i.e. unexpected age/cycle related faults, with less informative FDRs. The Airbus FDRs apparently record many more parameters, but this would be prohibitively expensive on older AC and still may not pick up relevant info.