[4RE KLR]

No it is not an internal noise, it is definitely an external noise.

When the car was new Cadillac had replaced the fan four times for similar problems. I feel certain it is in the fan. It is not the fan bearings. The fan turns freely.

It sounds like a piece of insulation, or wrapping tape, or maybe even a plastic tie-wire that is coming into contact with the fan blades as they turn.

I think it stops as we speed up because the wind coming though the radiator is pushing whatever is hitting the fan away from the blades.