cgm, that recording, were you stationary? or moving?
if it is happening when stationary, as well as when moving, you can cross off wheel bearings and loose stones in the brakes

my thoughts would lean towards something in or around the Flywheel area........????

get yourself a LONG long long handled screwdriver (or a stethoscope) and do what your LR mech was doing, just place it on the casing or outside of anything and stick the handle bit in your ear
around the front of the motor - for timing chain
around the back of the motor for noises from clutch / auto trans

anywhere that has moving parts - BE CARE FULL where you put your hands and the screw driver

but you WILL hear it eventually.

I hope you find it is an easy problem to sort.

cheers