Just some observations:
*Listening to the noise on the link, it sounds very much like a bad bearing or something hitting the fan blade.
**It also kinda sounds like a chattering contactor.
***The breaker the OP said was turned off was labeled "heat". This tells me that he turned off the AHU inside which has the LV Xformer which in turn would shut down the outside unit also.
****the better test would be as Steelman noted, turn off the disconnect to the outside unit while leaving the inside AHU running. This disconnect should be located next to the outside unit. This way the contactor will stay engaged while the unit stops due to lack of power. If the noise remains, it's the contactor. if it stops it's something with the units moving parts, ie; fan, compressor or combination.